I would shutdown and move the primary unit to the new location. In that way you could configure it for the new IP on that location and when you move later the FO unnit it should configure itself smoothly with some minor manual changes.
The standby unit should work with the config of the primary unit and should not cause an interrruption of the services.
I have never tryed this but this should work.
Please correct me if it should not.
sincerely
Patrick