The easiest that I have found is just flip what is reversed in the texture or use the right handed export. If the faces themselves are reversed then that has to be done in the modeling program. In milkshape select the faces the are reversed and press "crtl+shift+F" and the faces will face the front. In blender go into the edit mode and the edit tab and press flip normals and it will flip all front, but sometimes you will need to select the faces. But trying to do all of this in say the map editor, not happening or atleast I have never heard of it being done. Now if you my is just appearing back to you in game just go to the fpi and look for "fixnewy=" and put 180 and that will turn it around. I hope this helps.