Hi Rocco and George,
TestFlight invites can go out to any email, and you then accept them using your Apple ID on TestFlight. The email that was used to receive the invite does not matter. As long as you are receiving builds, you should be good and not need to change anything on that front.
Regarding this group, if you want to unsubscribe and resubscribe using another email, you can do the following:
Note that you will want to send the unsubscribe from the email that you are currently subscribed with, and the subscribe one from the one you want to be subscribed with moving forward.
Hope this helps, and please refrain from posting non-feedback under build topics.
Thank you again for testing!