1. Find your new model, for the example I'm going to use this one :

2. You must then think about which model is closest to its morphology, I will use the one that comes closest :

3.Import your starting model (that of Rappelz) and merge all the triangles together as in the photo :

4.Import your new model and now position it closer to your starting model :

5.Follow Image :

6. Follow Image :

7.Follow Image :

8. Pass both triangle in weight painting mode, after, select you model of Rappelz and CTRL+Click you new model triangle and go Transfer Weight.

9. after delete the triangle of model Rappelz.
10. Select you model and Ctrl + A = Rotate / Position / Size and export to nx3
INFO : it is possible that you have a problem, you will then have to go into edit mode and do: Remove Doubles then Recalculate and finally Add the modifier Triangulate and apply.
INFO 2 : This trick does not always work, sometimes you have to overhaul your basic model.
Preview of my model finish (sorry for quality, screen from virtual machine):

Good Luck






