@HerraBRE !OStatus (via /.well-known/host-meta and LRDD such as #) lets you create aliases on any given domain name. Your alias in !OStatus is just like #, any random string. However, implementations seem to assume it should be a full WebFinger ID such as acct:mmn@hethane.se (which is actually just the human-friendly way to address a lookup endpoint).

The main issue is that the aliases/redirects need to live for as long as people remember the old identifier. Which is likely to be indefinitely.