I don't extract textures from modded upks but sure, upk manager let u do that, the procedure is different but is easy, go to the "Mod files" tab and select (i mean, click the upk name and highlight the filename line, not click the checkbox) the upk that u want to extract the textures, after that change to "File Tables" Tab and go to the "export table" sub-tab, then select the file u want to extract, go to "File">"save Object As", you can extract one file at a time.