CoD Mod Friendly?

Hey all, just thought of a good question that I couldnt find an answer for.

Does anyone know if CoD will be mod friendly, by that i mean further than skinning. Well all know what happened with IL2 and that happend because people wanted to mod the sound effects in game and it just exploded from there.

Can this sort of stuff now be done "legally" with CoD but keeping the FM's locked still like can be done with most games.