For animated textures that consist of multiple frames you could either of course use sprites/ models instead, or manipulate the bitmap yourself:
Grab a pointer to the level texture with
bmap_for_texture(STRING* name),
then write into the texture using bmap_blit, bmap_process, panel.target_map or bmap_rendertarget and draw_quad or something like that. Whatever is more performant.

EDIT: Or just with a regular shader and pass your texture using the _bmap feature or entSkin1, if that works.