Trigun from Dirge of Cerberus

[Monkey D. Luffy]

While no actual STATS can be altered outside of Power-Ups or Alternate Forms, you can simply explain in the moves that one possesses higher power but less speed and longer reload time, another has higher accuracy but less power and shorter reload time, etc. Your stats will not be changed, but the moves will still maintain the effectiveness you have in mind.

Of course, if you're willing to spend the OM, you can purchase Alternate Forms if you're adamant about it.