There is a way, but the problem is that it's another mod. So you basicly have a choice; a really cool admin mod or a mod that lets you customize all attacks.
The mod I'm talking about is the Duel_SE mod which can be gotten at:
http://www.nitemares.de/duel_se/)
Personally I gave up the admin options for the gameplay and it's worth it(IMHO). But it's up to you of course.
But at the same time, maybe your players just need to practice and get better and stop whinning to you. :p As long as he isn't cheating or spamming moves to the point that it's ruining everyone's fun, I personally wouldn't worry about it. I mean the Red stance is already much slower than the others as it is, so lowering damage on it would pretty much make it useless.
Just my humble opinion:D