I still have ccexplore's hacked DOS lemmings exe which is better than custom lemmings simply because it allows for more levels.
However, the drawback is, I think the skiplevels cheats are removed, if I recall correctly. Then again, ever since I learned that CustLemm used Skiplevels, I haven't tried it in this one.
Also, you can rename the styles. This works quite well. Use 0-4 for the original and 5-8 for the OhNo! If I decide to use it, I make the Christmas Lemmings style 9. This should work with either OhNo! or the original. And CustLemm is still on the
The Lemmings Archive.