Because a few people have tried this already:
Please DO NOT try to replace another fedi instance with a GoToSocial deployment on the same domain, with the same username. This will almost certainly cause issues with federation due to public/private keys changing, and it is not something we support.
In the future, we’ll try to provide a proper migration path between GtS and other fedi servers. But in the meantime we recommend deploying GtS at a subdomain that hasn’t been in use yet, like
Your enthusiasm about GtS is appreciated! But if you try to drop-in GtS in place of a preexisting fedi server, and things break, we will not be able to help you with them.