I've uploaded the Lemmings Plus IV update.
In addition to making use of the two backgrounds options (and not having backgrounds on the special graphics levels), I also changed the music system to one similar to Lemmings Plus V's (ie: the musics relate to the graphic set, rather than a general rotation). Don't ask why, I'm not going to answer that yet. There's no special music for the final level of each rank anymore, but there is still a special music for the final level of the pack and for the special graphics levels (except Luck Of The Draw, which didn't have a special music in the first place). All the existing musics (except the rank-final one which was removed) are still in there, and there's three new additions too so that each set has two tracks.
The update remains compatible with V1.48(-B) and V10.010.XXX, so you can use it even if you haven't updated. You won't get the backgrounds on the older NeoLemmix version though (you will still get the new music).
EDIT: Lemmings Plus Flashbacks II has also been updated to reflect the changes in Lemmings Plus IV.
In other Lemmings Plus news... in all honesty, I'm just not finding Lemmings Plus Twists as fun to work on as I thought I would. So I don't know if I'm going to go ahead with this project, or just release the small amount of content I already have (almost all of which is just "the repeats from the old LPII / LPIII Bonus Packs that still work on new NeoLemmix versions").
But with that being said, I've begun work on another new project that'll be much more fun to work on, and in the few hours since I started on that I've already achieved far more than I have on Twists since I announced it. For now, the only thing I'll say about this project is that it is not Lemmings Plus VI, but is a Lemmings Plus pack.