Originally Posted by Dak Drexl
I don't see why not, but remember an mdl must be accompanied by an mdx if I remember correctly.
Dak is right, you need the .mdx to accompany your .mdl file. The .mdx contains different pieces of data pertaining to the model, so it's a compulsory thing.
Anyway, if you've got a new .mdl, you will have gotten the .mdx with it when you compiled. Just name them as appropriate and drop 'em into your Override.