Is there an easy way to swap out my RBR40 for a RBR50?

Sorry, no.  Congratulations on getting a good deal on the RBR50.  I am certainly happy with mine.

It is simple to add satellites to a router, because the satellites get the entire configuration from the router.  Alas, as far as anyone knows, the configuration file for the RBR40 and RBR50 are probably not identical, so it is not possible to export the configuration from one router and import it into another.  So, I would be prepared to set the RBR50 up from scratch (after updating it to the latest firmware!)

You can always give it a try.  i.e. on the Orbi web interface, under Administration, Backup Settings, "Save" the current configuration to your hard drive.  Then, when you connect to the new system, go to Administration->Backup Settings, and try to upload the saved configuration.  It can't hurt anything.  If somehow uploading hoses the router, just get out the trusty paperclip and stick it into the "Reset" hole for 15 seconds and the router will return to factory settings automatically.

If it does work for you, please report back.