Abandon unwanted registry changes without powering off PC?

Is is possible to undo mistakes to the registry (say I've been on one of my weekly purges and screw up ) without doing the complete power off option?

For example (complete guess here) would killing explorer.exe then regedit.exe and then restarting the shell not do the trick?

Anything done in the registry is "realtime". If you have WinXP or WinME you can use the System Restore feature. If you have Windows 98 you can use the scanreg feature in DOS mode and then choose View Backups and possbily restore one from there. Otherwize yer screwed.