To be safe, you'd do a factory image flash. That way you know you have a good starting point. There's the boot image, including the ramdisk, and radio (depending on what platform you're running on) that would have changed.
Or, if you're feeling lucky, clean wipe and flash your new ROM. What's the worse case scenario? You have to do it twice.
Three out of four voices in my head want to sleep. The other wants to know if penguins have knees.
First you forget names, then you forget faces, then you forget to pull your zipper up, then you forget to pull your zipper down. ~Leo Rosenberg