The tooth extraction went very well, although I've been bleeding from the mouth for about the last 7 hours. Doesn't hurt as much as I've been told it would.
So, the rules are: No more than 10 terrain pieces, no more than 4 new interactive things, and no more than 3 new steel areas, correct? Also, after making my addition, I should figure out how many lemmings are required to pass the level.
I'll try to figure out some clever addition I can make that doesn't completely mess up the solution to the level. Not sure when it'll be complete, but... it appears my surgery today had no complications and I'll be fine.