Changing email address won't break contact with the HDR-FOX - that is established by the "Unique Identifier", and I have three units registered to one RS account.
Surely the answer is to start using a new address before your old one stops working - then you will know whether errant emails are still arriving at the old address and need dealing with. The same applies for every other email migration you may need (including your address book). If possible, put your new address in the "Reply To" field of any emails you send from the old address, send from the new address whenever possible, and have as long a period of overlap as possible.