[makomk]

One of the ways in which admins often treat instances like their own petty fiefdom is cutting off communication with other instances that don't toe the line. So sure, you can move instances - just don't rely on being able to contact your friends anymore if you do. (Some instances even have a whitelist of instances that are allowed to follow and interact with their users, with everyone else blocked.)

[boyce]

It's rare to outright block an instance (for not moderating child porn or something of course but not otherwise really)

Instead most "blocks" are just muting from the federated timeline, precisely so that you're not cut off from contacts.