Wish I'd known of this sooner...
FINALLY my Demoness can have her horns a fixed part of the head model without me having to battle either freakishly large PLTs without sufficient colour channels, squash the horn textures to perdition trying to cram them into a PLT with everything else (which doesn't work) or use separate head-aligned vfx that have to keep being reapplied.
Thank you for this excellent discovery, OTR.