would a 20 unicycle frame fit on a 24 inch wheel set?
If the bearing spacing is the same, Yes.
a. No
B. Make your thread titles more relevant and giving information about your question
C. wrong forum, go to Rec.Sport.Unicycling for posts like this.
wah, my dyslexia must have kicked in, You can always put a smaller wheel in a bigger frame but not the other way around.
so let me refraise my earlier statement
No.
Nope, unless you meant to say would a 24" unicycle frame fit a 20" wheel. 
If not, 
On the torker DX it’s possible (but just barely). In general, no unless your 20" frame has 2+ inches of space, and the bearings are positioned correctly.