actually, it isn't your main chao, i don't think there is any way to know which one it effects. But i know it isn't just your main chao because i had 5 different chao and one of them is lv. 60 run, other is lv. 55 swim, other is lv. 57 power, other is lv. 60 fly, and the other was one i had just hatched and guess which one it changed... yep, the one i had just hatched; but before you start believing that it works on your newest chao listen to this. I tried a the code on my other memory card, which has 8 chao in each garden, some fly, some power, some nothin', etc., and some ones that had just hatched also, but it changed my nights chao "fly guy". i don't know why, but it did! Hope this helps.
~ Chaocrazy ~