This is wrong, in so many ways. I'll try not to rant too much on your friend, but here's my take on this:
This is a crappy way to get top dollar for your animals. You are putting the lives of the hatchlings at risk, for what? Higher coloration / wonky patterning? Then selling them to people (presumably) without ever mentioning that this little "trick" is why your animals look so neat and unique, not your blood lines / genes / hard work / quality.
Ball pythons can get some funky patterns/bright colors from a temp spike. They can also get kinks, eyeless deformities and still born. All for what? To make them a bit more unique, so people will buy them, but they hold zero genetic value as far as GENETICALLY improving said morphs/genes/whatever.
/endrant.
Sorry. This ruffled my feathers hearing a breeder would knowingly do this...I'm not trying to attack you at all OP. I apologize if it came off that way.