I sometimes open a jpeg texture in Painter and alter it somewhat: tattoos, that sort of thing. I would like to do the same with the Stephanie hi-res texture I just purchased but it is a mat file,(pz2) so there is no jpeg. Any ways around this?

a mat file is just a pose file that automatically loads textures on a model for you so you dont have to apply them manually.There should be a jpeg texture that the mat file points to that you can alter if you want.

If you don't know where the texture is, simply open that .pz2 file in Notepad and check out the file paths :)

After you have altered the texture, you can do new MAT file for your new texture. Take a copy of the "old" MAT file, open it in a text editor and replace the filename (and possibly path) from the old texture to the new one. Can easily be done with a "search & replace" command found in most text editors. Or, even easier, download the MAT Pose Editor form free stuff and use that to adjust the MAT file so that it loads your new texture.

check runtime/textures/daz/characters/stephanie/ and see if your high res textures are there. thats the defualt path for most of daz's hi res textures