You can use Interactive SQL to change the name of a multiplex server.
Prerequisites
Although you can run the
ALTER MULTIPLEX SERVER command
from any server in the multiplex, it is recommended that, like all
DDL, commands be run on the coordinator. Except when
altering role from reader to writer, the named server automatically
shuts down once the change is committed.
TaskStart the server, connect to it, and issue a
command in the following format: ALTER MULTIPLEX SERVER oldname RENAME newname
This command renames and shuts down the named server.
An alternate method is to right-click the server and select
context menu Control > Include/Exclude.