A musical associate of mine would often take songs he'd written in one genre and then try to arrange the same song in a differnt genre. This would often force him to change some lyrics, add different passing chords, etc.
As a result, he would at times come up with a "better" song - and at a minimum, it would force his to think and compose in different genres.
This can also be an effective tool for a writer that is suffereing temporary "writer's block" - rather than trying to creating a new song - sinply "re-create" an old song.