If for example you used my Rangers ;D , than all you had to do, was to replace the old p3d file with the new one from Resistance (don't recall the name of the p3d file to be honest), rename the new p3d file with the exact name the old one had, something like PORUs75thRangersP3D.p3d (not sure again you'll have to check that), than use the Textures Swap Utility tool in the p3d file to change the textures path (from data\texture file to porus...\texture file) and that will do the show.
Later in the cpp file, add the hand gun and the mags.
However if you manage to change the p3d send me a PM and I'll send you a fresh new cpp file, with my boys equiped with Flippers weapons and hand guns)
Cheers,
Skaven