You'd need to redefine most of the animations on a soldier, aswell as editing those anims..
You can't invert them in OFPAnim, you may be able to in Maya, but then you need to import the anim, invert it, convert it back. Quite fiddly, about 100x more if you've not used Maya before
It's a LOT of work anyway, but not impossible. VME replaced almost all animations for their soldiers
- Ben