There are two solutions around the Cheapo problem:
1. When you open the level and it says "Select Style", click the drop down arrow, and select "NeoLemmix - Cheapo Styles".
2. (more convenient solution IMO): Just put all the graphic files in the NeoLemmix folder instead and open the level as normal.
Looking through the ROTL, the only easy repeat levels in the game are:
Picnic 1-10, 13, 15, 17-20, 22-25, 27-28, 30
Hootenanny 5
For me, I'm in favor of removing Picnic 1-9 (the tutorial levels), 19 ("Hunting Season", repeat of "Wish you had them?" Carnage 4 and 20 "Food For the Gods", repeat of Carnage 27 "Finding a Safe Place to Stay"). If we remove Picnic 6 which is "Play Bridge", we could replace that with the original version of Play Bridge (this version has 20 builders).
I'm thinking that if you want to keep Ups and Downs for its talisman, perhaps you can replace "The Endless Steps" (currently Hootenanny 17) with that? IMO "The endless steps" is too easy with instant bombers.
Regarding ccexplore's level, did you put the x_vgaspec0.dat in the NeoLemmix folder?
Also, a level I'd like to be brought back: "Conveyor Bolt" by Ellischant.
EDIT: Found another Picnic-worthy level: Blowtorches are Fun by Mossaic91.
EDIT 2: Turns out I put the wrong level for Tumble Weed's Skill Your Lemmings (it's And Out Come the Bashers...). Here is the correct version.