Yes you can use 3/4 cup (180 ml) of light/dark corn syrup:
You can use any of the following substitutions:
1 cup of honey
3/4 cup (180 ml) maple syrup plus 1/2 cup (100 grams) granulated white sugar
3/4 cup (180 ml) light or dark corn syrup plus 1/2 cup (100 grams) granulated white sugar
3/4 cup (180 ml) light molasses plus 1/2 cup (100 grams) granulated white sugar
1 1/4 cups (250 grams - 265 grams) granulated white or brown sugar plus 1/4 cup (60 ml) additional liquid in recipe plus 1/2 teaspoon cream of tartar
Courtesy of Joy Of Baking
Honey contains lots of aromatic compounds, which are quite big, fragile molecules. This is one of the reasons why cold centrifuged honey costs more. When you decrystalize honey by heating it, many of these aromatic molecules break up, and you lose the complexity of the aromas. So yes, it is bad for the honey. Also, it may reduce its health benefits, as vitamins and other micronutrients tend to degrade under heat (but only some of them - others, like trace minerals, are quite unimpressed by temperature).
Of course, the question is not only if it is bad, but if it is worse than eating crystalized honey. This depends on 1. The honey quality and 2. the way you plan to use the honey. With the honey quality, it is obvious that, if the honey has already been heated in the production process, the volatile stuff has already been destroyed, so subsequent heating for decrystalization is not a problem. But if you spent money on cold centrifuged honey, you are negating its benefits by heating it.
About the use: If you will heat it anyway (as in putting it in tea, or baking it into a dough), there is no reason not to decrystalize first. Also, if you are only using it as a sweetener, even cold, there is no problem in heating it. But if you are using it as an aromatic agent, like in a creme fraîche and honey dressing for a fruit salad, or using it as a bread spread, then it will taste better if never heated. It will still have a general honey taste and aroma, but the subtle notes will be missing. Whether this bothers you or not depends on whether you rate aroma or texture higher. My personal choice is to not heat honey in these cases, but your preference might be different. Probably the best way to decide is to take a small amount of crystalized good quality honey, heat it, and compare it side-by-side with the crystalized version. Then use whatever version you like better.
If you happen to like the decrystalized one more, it is probably a good idea to not spend money on fancy honeys in the future ("cold-centrifuged lavender honey from South France" etc.), as it won't taste all that different from a common wildflower honey after decrystalization.
Best Answer
The answer, quite simply, is no. Even advanced laboratories have difficulty making the determination for certain.
This is also a complex problem that gets more difficult as various standards are used and then fail. Before 2000, a common solution was to simply use microscopic analysis to look for pollen and and other vegetable matter. Since then, many honey processing plants have been developing increasingly advanced filtering techniques that will remove the characteristic markers (deliberately or unintentionally). [**See detailed note below.] Various chemical or basic physical markers also have proved insufficient, since the sugar composition of honey can be faked quite well with various sugar syrup blends.
The accepted standard these days, as mentioned in the question, seems to be to use a mass spectrometer to determine the carbon-13 to carbon-12 isotope ratio in a rather specific lab procedure. (Obviously most people don't have a mass spectrometer at home.) The current procedure for this test was adopted after previous lab tests were shown to generate false positives in some batches of honey. The isotope ratio method is the only one specifically listed in the FDA's import alert to determine the possibility of adulteration:
Ironically, in order to avoid the previous false positives for the New Zealand honey mentioned above, the new testing process needs to have the pollen completely removed, a process which has also been used to hide the origin of honey and to confuse analysis:
But even a refined isotopic methodology is flawed when it comes to detecting various types of adulteration, specifically beet sugar. As this article notes:
So, what's the alternative? Well, the other general method that could detect various adulterating components is differential scanning calorimetry (DSC). This article gives a good summary of the process, which essentially looks at how a material behaves as it undergoes thermal changes. At certain temperatures when crystallization or something occurs, there will be excess heat absorbed or given off compared to at other temperatures. And at other points there will be minor changes in heat capacity (i.e., the amount of heat it takes to alter the temperature of a substance by a specific number of degrees).
Honey, for example, displays a glass transition temperature (Tg) around -40°C (-40°F) near a certain point in crystallization. Other sugar syrups may not show this, but they may show changes at slightly higher temperatures (still below freezing), due to water crystals freezing or thawing. (Water is included in the sugar network in honey, so it doesn't show the same characteristics.)
There are other thermal properties that can be measured at various temperatures. As this article summarizes in its conclusion:
I would pay particular attention to this final sentence -- the differences can only be detected "under laboratory conditions" where precise temperatures and amounts of heat can be measured. To replicate such a test at home, you'd need to be able to add a certain precise amount of heat to the honey at subzero temperatures, all the while keeping it isolated from other sources of temperature fluctuations and observing where the heating "stalls" briefly. Then, you'd have to calibrate your homemade test against some known samples (syrups, 100% honey, etc.) just to be sure you're actually observing the same things as in the article cited here. You'd need to confirm that by observing a more subtle difference in heat capacity changes that would occur in hot temperature ranges (below boiling).
Even under lab conditions, this sort of testing has a threshold of 5-10% adulteration, and that requires something like being able to detect the difference between a glass transition onset at -41°C vs. -42°C. Also, it should be noted that these physical characteristics are inconsistent among various batches of honey. In this study, for example, the Tg was found to have a variance of over 7°C in different pure honey samples. In the study quoted above, that range of 7°C would indicate a difference between pure honey and a 50/50 mixture with a sugar solution. (If you look around at other studies, like this one and this one, you begin to see a Tg range that is well over 15°C for various pure honey types.)
I'd guess this is partly the reason why DSC isn't generally adopted as an official testing procedure: to use it effectively, you'd need to really know the specific kind of honey you started with before blending with adulterants, and most of the time you don't.
Bottom line: there's just no way to do a test like this at home.
Finally, to address a point raised in the question, based on the DSC data there should be minor differences in honey's behavior at various temperatures, perhaps even how fast it dissolves at a certain temperature. But the differences are so small and/or inconsistent among different types of honey or different types of adulterating components that there's no practical way of consistently identifying them outside of a lab environment where very precise conditions and measurements are possible. It might be possible to isolate adulterated samples outside of a lab given prior knowledge of the original honey used and the specific adulterants that might be present, but that information is generally not available. If it were a simple matter of a test like "let's mix this honey in some water and measure how long it takes to dissolve," government regulations would not be resorting to mass spectrometers to try to detect adulteration.
Note that this answer really only "scratches the surface" of the various testing methods available. Here's a partial list of possible tests. Even a cursory search will uncover hundreds of scientific articles describing the advantages and limitations of various tests. Note that most of the other tests only detect specific kinds of adulteration and/or are mostly used as initial screening tests that then need to be verified by another lab procedure. As mentioned, the current standard seems to be an isotope ratio test.
** ADDED CLARIFICATION ON POLLEN AND FILTRATION: Some pollen is generally removed in the normal filtration process used to produce a "clear" honey that doesn't crystallize quickly during storage. However, traditional filtration techniques often allow trace amounts of pollen to remain, while some processes may use a more complex "ultrafiltration" method that will remove all pollen traces. The reason for complete pollen filtration may have originated with a desire to disguise the geographic origin of honey, whether pure or adulterated. In 2001, for example, the U.S. instituted high tariffs on Chinese honey, to avoid putting American beekeepers out of business. At other times, various countries have instituted outright bans on honey for periods due to contamination or adulteration, such as the EU ban of Indian honey in 2011-12. Such actions have provided strong incentives for Asian honey producers to disguise the origin of honey, even if it is unadulterated. The result is that large amounts of commercially available honey are now filtered to remove all pollen, which has a side effect of making adulteration detection much more complex. That said, it should be noted that normal filtration may also result in very low or undetectable amounts of pollen, so the absence of pollen is not necessarily evidence that any deception is intended. (See further details and explanation here.) However, processing methods that deliberately remove all pollen have been used by those who wish to disguise origin and/or adulterate honey with cheaper substitutes. The question specifically inquired about Asian honeys which had been diluted with water; given that ultrafiltration often involves adding water during processing and has apparently been used by some Asian producers, I originally wrote my answer to target the specific honey type inquired about. Once again: an undetectable level of pollen in other countries and from other producers is NOT necessarily evidence of anything nefarious.