main question is - how much efforts/difficulty is involved. 'cause i'm total noob in modeling and if it's quite difficult probably will have no chance.

there is an infantry unit that has ATGM weapon but infantry model is "not suitable by looks". i wonder how difficult it is to take other infantry model and "insert"/exchange current infantry part. animation is the same, but i don't know what about bones..
maybe experienced modellers will say that to make a new, desired, model is better solution, but it's over my abilities.