It is very possible to change the dialogue and models, very easy to do, however changing every text in the game may take awhile. As for models...it is very easy to create (low poly models) for the game...you wouldn't want a advent children like graphics into the game anyway...looks awkward with the bone animation (blocks), as well as it looks out of place. As for changing the animations for the field models, example such as tifa's for clouds is not possible. or if you tweak the stand animation...everyone else would look the same way, since they all use the same animation. Battle animations, you can only change the animation of characters you can use, sephiroth and the default playable characters. But the limit animation will either screw up, or just doesn't work and freezes.