I'm sure every packager has come across this situation: something breaks and you need to bump the RPM spec version number automatically, here's the trick:
$ rpmdev-bumpspec -r --comment="- rebuild against correct tag" F-1{1,2,3}/*.spec
Above you see a real life example, we needed to rebuild all KDE packages against the correct tag in Fedora F11, F12 and F13. What this command does is that it bumps the version number right after the %{?dist} tag and generates the respective changelog entry.