Yes, and it is very easy. I do it all the time.
You only need a very simple calculation. You don't even have to be precise.
If you do want precision, you will have to find out 1) how much of your flour protein is gluten, 2) how much of your "vital wheat gluten" is gluten, and 3) how much gluten content you need for your recipe. Then use a simple rule-of-three calculation to get the amount needed to add.
I usually don't bother, because 1) and 2) is information which is very hard to find, and due to the large difference in gluten weight and complete weight, imprecision from not using true proportions is minimal. What I do is:
- Look up the protein content of your flour (usually printed on the package), for example 9.6 grams per 100 grams
- Look up the gluten content needed for your bread recipe. If it is not specified, 12.5% is usual for bread flour.
- Add the difference in vital wheat gluten. In the example above, add 2.9 g of vital wheat gluten per 100 g of flour.
This doesn't produce exactly 12.5% gluten content, but I think that it is within the tolerance of most recipes; indeed, not all commercial flours are exactly 12.5%, they vary with brand and season.
I add the powder to the flour and mix it well before making the bread. If I am using a preferment, I add all the gluten to the preferment and make the non-fermenting part with AP flour only, so my gluten can benefit from longer autolysis.
I have no direct comparison with "true" bread flour, as I have never used it. But my breads requiring bread flour turn out good for my standards. There is no problem with bad distribution, the dough turns out very smooth and evenly elastic. There is a pronounced difference to using AP flour only.
The big question you have to ask yourself is, "How absorbent is what you want to add?" For instance Chia seeds are not going to affect your hydration much. Those you can probably just add. Corn meal on the other hand will absorb water, but it won't create gluten. You'd want to replace some of the flour with corn meal and perhaps a bit more vital wheat gluten. Wheat bran contains gluten, oat bran does not. Both will be absorbent so should replace flour. Any cereal will be absorbent, the question of gluten will depend upon the grains used. Because you're using a bread maker you're probably not as intimately aware of the hydration of your dough as you would be if you did your kneading by hand. For your next few loaves, take the dough out of the machine when it is done kneading. Give it a few kneads to get a feel for it. You'll feel it if your hydration is off.
You're right in that you want to try adding one ingredient at a time. Also start small, you might just be surprised at how much 1/4 cup of corn meal will affect your loaf.
I find it helpful to look at recipes that include the ingredient I want to add and compare that recipe to similar loaves that don't contain the ingredient. In what other ways are the recipes different?
2 websites come to mind that you might find helpful.
The Fresh Loaf and King Arthur Flour
Best Answer
They make whole wheat flour, but their bread flour is definitely refined; it does not contain bran or germ. Their bread flour is milled from a specific hard red spring wheat from North and South Dakota. That particular wheat is higher in protein than the wheat and wheat blends of other brands of bread flour.
KA's whole wheat flour (not the white whole wheat) is also milled from hard red wheat, but it's unclear if it's the same "hard red spring wheat" as in the bread flour. The protein level is higher in the whole wheat flour than in the bread flour.
Notice that the bread flour is enriched (see the ingredients), as is required by US law for refined flours. The whole wheat flour is not enriched.
You might find this information regarding whole grains helpful: What is the meaning of the term whole grain? Notice from the graphic that there is not a lot of protein in the bran and germ.