ok sorry for posting when a year has gone by but yes there is a way
this is what someone from filefront told me hes name tiro1000
First you need to have the ability to go into a pk3 file. got that? good.
Now you need to go into the assets1 folder, into models, players, and then you need to find the folder name of the character you want to replace. Then, you make your own folder for models, players, and then put the same folder name for that character.
Go into the pk3 for the new model, models, players, and the end folder, copy all of the contents, and post them into you're new mod folder. Pk3 it up, put it in your base folder, along with the model that's replacing it, play game