Are you talking about online compatiblity or mod?
You can do a OC by replaced the
GeometryName = "cis_weap_inf_rifle"
and put the tat_weap_tuskrifle.MSH in the MSH folder of the CIS (and the Tga that goes with it)
A Mod would be getting the ODF MSH and TGA of the gun you want, putting them in the CIS directory, and typing the gun name in the charectors weapon slots.