go to the leiningen repo, browse the tag corresponding to the version you want, download that bin/lein file

you can name it as you wish e.g. lein or lein-alt . upon first run it will download any needed internals

Awesome. Let me try.

and you can run lein upgrade 2.9.4 with that script to set whichever version you need

the versions of lein installed through package managers don’t allow you to change the version

if you use asdf there's a plugin for it https://github.com/miorimmax/asdf-lein

you can set a .tool-versions file per project so it automatically selects the right version for you