Originally Posted by
YourMaster
Hello, welcome.
The keeperfx\creatures folder is indeed the one that's being used for the main and most custom campaigns. But keep in mind that you'll only notice changes when you start a new game. So if you load a save, or even just press continue and start the campaign level fresh, you still get the old values. The save files have the configs stored inside of them.
One important thing to note, is that the original game had several bugs related to stats, which particularly harmed strong, high level units. A level 10 reaper in the original game was quite the weakling, almost all of his attacks would miss, he couldn't keep his speed up, his health and strength were limited beyond a certain point. So many of the stat changes you'll see are actually to compensate for the bug-fixes in keeperfx.