Another Option For Textures In Linux
Thanks again to Pekka and ericw for the advice and recommendations above. Just wanted to say (just in case in might be useful to someone else) that I got TexMex to run in Wine.
For this I have to thank Luneran again, who initially recommended TexMEx to me
over two months ago. Back then I saw "Windows only" and didn't investigate further -- don't know why I didn't think of trying it via Wine until now!
Admittedly I haven't tried doing anything too crazy/complicated, so I cannot vouch for medium/long-term stability, but at least for exporting and importing one texture from one wad into another, it worked like a charm and was very user-friendly/idiot-proof.