Sergbuto wrote a retexturing guide (use the Wayback Machine (archive.org) to see it):
http://web.telia.com/~u18216264/Retexturing_Guide.pdf
It references tools by Covet and Ortega. Ortega's GUI was available here (again, use the Wayback Machine to see the page):
http://www.mp-labs.com/sh2mods
JRFTexMan10e.zip (English)
JRFTexMan10.zip (Spanish)
Unfortunately, the download links don't work, and I don't have copies of the files. It might pay to check SUBSIM's downloads section to see if these tools are available individually or as part of some package. Sergbuto had them listed as Pacific Aces tools in a sticky at one time.
Good luck.