Hold your horses - or at least create some backups.They use AWS. Amazon has the best global web services. MS is faster, but more expensive I think.
If it can't handle, it will scale up until it does. This can take an hour or to for the "push" to their network.
I was able to change the Alt's game email addy during initial login to Frontier Launcher.
Guess we shall have to copy the custom binds file over to the new install now.
@Arsen Cross in https://forums.frontier.co.uk/threads/epic-games-accounts-rules-considerations.558787/post-8802252 thinks this shouldn't be necessary (from what I understood).