yes but it takes a helluva lot of work cause you've got to reverse all the bone rotation/translation keys for the animation sequence you're editing and if it's a model with lots of bones it's very tideous and easy to make a mistake
If you retoated the bones wouldn't the model get screwed more cecause certain ares especially limbs the feet would be pointing backwards and therefore he would fall on his heel first and so it would just look messed up instead.
PS - i know nothing of mdl's and this is the thought of a complete noob at mdl's
spell effects often use particles and/or ribbons. For particles just set their speed to a negative value. For animated ribbons you have to change the bones movment. Something which is very tideous.
