DJENKINS1973,
Easy way, no.
Somewhat time consuming way, yes.
You can export out the Greetings you want to work with and then just do a cut and paste into the other mailbox and load it back in. I have only done this a couple of times back around 2.3, but the process should be the same; although not fun at all since you may have to do it a couple of times. Make a backup of the mailboxes you are working with just in case you mess something up and need to set them back to what they were before you started.
Thanks,
Steven