The work around is to use 3dsimed to import the gmts and save as fbx, import the fbx into max 20XX, do the modification to your mesh and or texture and save as fbx. Re import in to 3dsimed and export as RF2 gmt or if you still have the old RF2 gJED app, you can import the fbx and export as gmt
Yes, Ive tried it and it works. In 3DS Max 20XX you setup your materials as standard, add the diffuse, spec and norms textures accordingly, and export as fbx. When you load the fbx into the editor, either gJED or 3DSimed, then you can set the shaders etc. as required. Cheers, Hope this helps