OR, after changing the ID, have the instance publish a “domain_change_notification” that all federated instances would be listening for and then they would update their data.

ah ok. well then there would need to be a deeper change and all instances would need to update. have a field for the ID of the instance itself, and a field for the domain. or something like that. would that work?

i don’t think that that would be too difficult to implement

AFAIK there is no reasonable way to update/change this. IDs are forever.

can’t you just run a postgresql query to update all the post ids?