If I understand correctly, what you would like to do is copy the entire appointment entry to a new date. I don't believe that the BlackBerry calendar is capable of doing this but PocketDay has this feature.
To quote their web site: "PocketDay is a full featured Today Screeen, Personal Information Manager and Utility application suite developed specifically for BlackBerry devices."
I am currently using it on a trial basis. It's a great way of conbining your upcoming calendar events with your to do list, missed calls, emails, ect all in one view. It also allows you to select a calendar event and copy it to a new date.
You can download a trial version at PocketDay