Well, one option is to release it as an entirely new module. The advantage of this is the people looking to upgrade can do so, and everyone else can putter along with their stable legacy code. You could put a reference in the original module's documentation about the new module and explain the improvements.
Otherwise, you probably just want to make sure it's as backward compatible as possible. If it's not that popular, it's less of a risk introducing changes.
Three thousand years of beautiful tradition, from Moses to Sandy Koufax, you're god damn right I'm living in the fucking past
