Erik Darling wants to create a DDL trigger in tempdb which survives after restart:
One workaround is to create it in model. Then it will be in tempdb on restart, but it will also be in all the databases you create.
That may or may not have the intended effect! If you don’t want people doing a certain thing in just tempdb, you have to add an additional check using the event data.
Click through for more details, including a couple of sample scripts.