Yep, you can retexture everything.
First method is to just simply modifiy the .dds file for the model.
Warning: Be sure to keep a copy of the original, unmodified
.dds file though in case it all goes horribly wrong or better still
copy the .dds file and FPE (or FPS etc.)file to your user folder,
of course remembering to modify any path information for the .x file
in the FPE (or FPS) file.
Second method (and probably a bit pointless really) is to load the
.x file into your modelling program and re-export the UV map. The
only advantage of this is that it will give you a clean, outline
UV Map on which to place your texture rather than trying to paint
over an old texture.
Obviously you will need a .dds plug-in for your paint programme, or
save your new texture map as a .tga file of the same name and delete
the .dds file, of course making sure that the FPE file points to
the .tga file and not the .dds file.
NOTE: If you want to use alpha transparencies in your texture
maps then you will have to save directly to .dds anyway so it's worth
getting hold of the correct .dds plug-in.
Hope this helps in some way.
Best Regards
Jason
Owner - Music Genius Publishing
http://www.musicgenius.co.uk