So a little while ago I saw a couple posts regarding the fact that one is never really "finished" with a song, but rather just putting it on the back burner for a while. I completely agree with this concept and I think it would be a good idea to dedicate a thread to it.
Post your strategies, secrets, mommy issues, etc...whatever you find helps you with reworking previously written music.
I use LSDJ (so far...checking into Beepola as well in the near future).
A thing I do a lot is clone a chain, say from the noise channel, then throw that bad boy into a Pulse channel.
...Okay, now hear me out.
As anyone who uses LSDJ would expect, it'll sound like completely horseshit. But after changing instruments, messing around with all the different commands I can 9 times out of 10 create something that I'm impressed with. Cloning the noise over into a Pulse really helps make more phrases which are basically derivatives of previous ones, but can sound much different while still actually fitting. It definitely helps vary up a song.