what happens when you issue ALTER SERVER in a hot environment?

[AC Gomez]

If you issue an  ALTER SERVER command and there are active connections with
that server in use or new ones are coming in, what happens? Docs on this
command say nothing regarding active processing using the server context
and changes to it. So I assume it's just handled. For example if you alter
user/password, I assume that as long as prior user password is still good
that actively running processes will keep going.