Just decompress the .a2c file and look for the texture – it’s (nearly?) always in .png format. I recommend using 7-Zip - WinZip usually (always?) won’t decompress the texture file. (WinRAR also seems to work but I haven’t tried it much.)
To just take a quick look at a skin, just add a billboard with any old texture (256x256 pixels is a good size) and then use the object's skin as a texture for the billboard. You can actually print out this image, edit it and import it back as a new skin - but the dimensions get stretched a bit and the mapping of the new texture to the underlying mesh may be a bit off (and - by Murphy's Law -
always at the most critical point.
)
By the way, you don't have to edit all of the new skin - just use the old skin for the sub-parts in the hierarchy you don't want to change. (Obviously you have to change the lowest parts in the hierarchy last.)