Our models need skins of course - these skins are images in jpg, png or tga file format. They should be in the same directory as the model (the md2) (somewhere below base/models/. You should enter the skin path as .skinfilename. The game will know to look in the same directory as the model for any jpg, png or tga file with that filename. The dimensions of these images should always be power of two.
To change the filenames of the textures or the amount of available skins you maybe (depends on the model format) have to edit the model files.
To change the filenames of the textures or the amount of available skins you have to edit the md2 files.
There is a perl script available for that in src/tools called md2.pl. With this tool you can change the texture sizes, upgrade the number of skins & change skinnames.
You need a Perl distribution to be able to execute the script. A good one for Windows would be ActivePerl.
Be careful. The tool/script is not able to downgrade the number of skins in the md2 file, just to upgrade them. To downgrade this number you have to edit byte 20 with a Hex-Editor (see md2 file/header definitions).