Hello,
As you have mentioned yourself, It was a long time ago and I don't remember much. Plus, I never did try to convert any of the models back. I am 99% positive that it is possible - you'll need the right tool-set though. I am not sure what tools are available for "Combat Arms", but as far as I remember there is an extensive toolkit for NOLF2 (which uses the same engine, more or less):
No One Lives Forever 2: A Spy in H.A.R.M.'s Way Toolkit for PC Download at GameSpot
You'll need the game itself (NOLF2) to install the toolkit though (which can be a problem). Also, you may want to take a look at these forums (
NOLF 2 - Mods & DEdit - The Glue Factory
) and search for anything related to LTA\LTB tools\plugins.
Hope that helps.