That is not sound because you're changing a fundamental aspect of them-changing them to fit your needs instead of treating them as they are despite the new changes.
This would be valid, but the only change I really want to make is to Nightstalker, my Sableye, which you will be changing anyway. i.e. You guys are changing a fundamental aspect of my pokemon. Now, I'm not getting up you for doing so, since Stall breaks things in weird places. But, on the other hand, this was my oppurtunity to make Nightstalker my Sableye again, and you guys attach a 15 point price tag on it.