You may be interested to know that when you install the Pro Pack, you get .png's instead of .rsr's (although any rsr.'s already there remain as well, but you can just delete them as they're useless). With Pro Pack you can just render your character or prop or whatever at 91x91 pixels, export the image as a png. file to the proper folder, name it identically to the thumbnail you want to replace, and that's it. A rendered thumbnail, transmaps and all. A very interesting new feature that to my knowledge remains totally undocumented.