Honey changing into unusable, hardened clump

If the honey has always had a water content below ~18% and is continuously stored in a sealed container (for instance a glass jar), it is perfectly safe to eat as long as you are over 1 year old. In fact, pasteurized honey is inferior in quality. The pollen and spores will remain in there either way, even if they're dead and can only be removed by (expensive) filtering. So if you got an allergy to that, don't eat honey. But they (pollen, yeasts) are not generally harmful. Botulism is not a concern unless you take medication that reduces the amount of acid your stomach produces.

Acid inhibits the growth in the stomach, your (good) bacteria in the gut (after the acid has been neutralized) will then continue to protect you. Since infants don't have sufficient/stable composition of bacteria yet, they are in (higher) danger of getting botulism. But even then, they rarely get infected. No point in taking the risk, tho.

Honey is hygroscopic, meaning it will draw moisture from it's surroundings (hence the sealed container). This effectively prevents pathogens to grow, preserving the honey as long as the water content of the honey remains at or below 18%.

In fact, here in germany, honey may not be subjected to temperatures higher than 40°C, it may contain no additives at all and the only thing you can do to it is filter the pollen out. We still don't have waves of botulism from honey here. In fact, I have never once heard of one.

This is most likely referring to honey processed without any heating, often simply called raw honey, or possibly cold-extracted or cold-processed. It likely has more flavor and color preserved than commercially-processed honey (which uses plenty of heat), but it may not be much different from gently heated honey. It's not actually cold (honey flows really slowly when cold), just not heated.

There are two primary ways honey would have been heated during processing. First and most common, most commercially sold honey has probably been heated substantially (perhaps up to 165F - 73,89ºC) to help melt crystals, allow impurities to separate, and to make sure everything's dead and safe. This definitely does affect the honey - it makes the flavor a bit more mild, and the color a bit lighter.

If you're getting honey from a very small producer (maybe someone with a hive in their yard), it's also possible that they actually heated it in order to separate the honey from the beeswax. The most effective way to get honey out of the comb is to remove the caps and use a centrifuge to spin the honey out of the frames, but for hobbyist beekeepers without access to an extractor who don't want to just crush and strain it, another method is to heat the comb, letting the melted wax (it melts around 145F - 62,78ºC) float the top for easy separation. This is pretty gentle heating, and doesn't have nearly as strong an effect as the commercial processes.