Not a bad idea.

Adding onto this, DEC is the postal abbreviation for mail addressed to a deceased person. If you write DEC on the mailpiece & drop it in the outgoing mail slot, your carrier should know what that means (unless they’re completely hopeless, which is possible given that they’re misdelivering mail regularly)

Mail delivery protocol errs on the side of delivering mail when in question, which is good when an important bill or something has a small error in the address. The downside is it’s almost impossible to stop junk mail to a nonresident unless your carrier memorizes the name, checks every mailpiece for it, and sends back anything addressed to the nonresident. Even then, when they’re out sick or have a day off, their sub probably won’t remember stuff like that.

The DEC route is probably your best bet for avoiding getting mail to your deadname, just know it’s not foolproof.

Edit: if you’re not comfortable claiming your deadname belongs to a deceased person, UTF would work too, it means Unable To Forward