Before you start changing textures, you need to extract them from Relic's SGA files. There are a few tools for extracting SGA files, one of which is my SGA Explorer. The Explorer has been out for a while, but I'm now putting a bit more work into it.
The most important change for DoW skinners will be that the SGA Explorer will have a "extract type" option where you can extract (for example) all WTP files from a folder and all sub-folders.
It's currently possible to extract just one type of file by using the 'Detail' view and then ordering by type and then selecting the now continuous list of files of the type, but it doesn't do it for sub-folders and it's not as user friendly (I think some people haven't noticed the functionality).
The other addition is going to be CoH (Company of Heroes) SGA support. DoW SGAs are v2, where as CoH uses v4 SGAs. There's a few changes in there that I've now got working, and files will all extract correctly (even from a 1.5GB SGA that came with the demo!), but there's still some data in there that I don't know what it is.