ieatmonkeychow, you're way is a bit off-the-road I guess...
All that has to be done, is just extracting that model from the .pak file. Can be done with Wally or HLMV, easy.
If you want to use it in your mod as an enemy, you'll need coding. No way around that. Well, maybe you can use it as a replacement model for the normal grunt but then it's just gonna use mp5 firemode, although it'll look different...
Changing the .fgd has NO effect on the game. The .fgd allows the mapper to choose entities and insert them easily into his level, but it all depends on whether the game code recognizes those entities and their settings.