For instance:
Old: 4 Balls
http://fantasticcontraption.com/?levelId=20
New: More than 4....
http://FantasticContraption.com/?levelId=9478
In your edits:
1) Make sure it's solvable.
2) Change the way it's solved... for instance in my 4 balls edit, a conveyor belt doesn't work nearly as well as it does in the original, so the player is forced to rethink how to solve the level.
3) Don't defeat the original feel of the level, however. Make it obvious it's an edit of a level and not a brand new level all together.
List of Levels:
Rolling Away: http://fantasticcontraption.com/?editId=91
Reach Up: http://fantasticcontraption.com/?editId=55
Mind the Gap: http://fantasticcontraption.com/?editId=16
Junkyard: http://fantasticcontraption.com/?editId=102
The Wall: http://fantasticcontraption.com/?editId=31
On a Roll: http://fantasticcontraption.com/?editId=89
Full Up: http://fantasticcontraption.com/?editId=88
Higher: http://fantasticcontraption.com/?editId=86
Around the Bend: http://fantasticcontraption.com/?editId=100
Up the Hump: http://fantasticcontraption.com/?editId=17
Mission to Mars: http://fantasticcontraption.com/?editId=62
Up the Stairs: http://fantasticcontraption.com/?editId=19
Big Ball: http://fantasticcontraption.com/?editId=23
4 Balls: http://fantasticcontraption.com/?editId=20
Down Under: http://fantasticcontraption.com/?editId=24
Awash: http://fantasticcontraption.com/?editId=28
Handling: http://fantasticcontraption.com/?editId=69
Tube: http://fantasticcontraption.com/?editId=76
Back and Forth: http://fantasticcontraption.com/?editId=60
Unpossible: http://fantasticcontraption.com/?editId=54
U-Turn: http://fantasticcontraption.com/?editId=4575
Cheers!
path on the far right...I don't think there's enough build room for the third one though 




