yeah, I try to do this kind of stuff too. But mostly, to practice, I get fake books or just a simple tune like "Autumn Leaves" with obvious harmonies and try to make something on Sibelius.
I have tried to do small stuff, like "writing a cadenza for a concerto" in a number of Liszt's pieces (ossias for Les Preludes, Faust Waltz, Czardas macabre etc.), but I kept finding that after hours and hours of messing around with it, I realize it was most effective just the way Liszt wrote it. The man could write and play anything; it's pretty hard to make something new from an already well-done work and be satisfied, because you can't help but compare it to the original.
Liszt comes to mind, and I have the fingers to play his music, but I was hoping for somethink slightly more esoteric, as modern performance practice dictates that we can't change what's written on the page. I'm not planning on performing any of this per se, so I suppose the real reason why I want lesser known music is to A. broaden my musical horizons a bit and B. so if I end up getting assigned something I've messed with later in my career I won't have a warped mental image of the piece.
I had to look up "esoteric" to understand what you were getting at. If you like Liszt, go for arranging some of his stuff! Don't worry about getting a "warped mental image" of a well-known piece. Most probably, thinking about places to take the piece will only enhance your understanding of it.
What pieces were you
wanting to mess around with, that is, ignoring your inclination to go with lesser known pieces?
Topic: I want some music I can mess around with