Do a search for the old Doom and WipeOut WAD extract/rebuild utilities. Look for the Wipeout custom soundtrack kit.
The WAD/DAT files are pretty much just big tarball files (like taking all of the files in that should be in the WAD and just attaching them one after another to make 1 big file - no compression). There was a professional grade extract/rebuld program that was making the rounds on the less reputable PSP sites that would let you swap out resources and rebuild on the fly, but I can't remember the name and I lost the zip, but I remember it was expensive. Hope that helps.