Terraspace documentation regarding terraspace "env variable"?

Related PRs:

RE: we cannot add dynamically (multiple) new ones or can only use the :EXTRA one for the whole project?

Believe a boot hook can help with that. Take a look at Boot Hooks - Terraspace

With the boot hook, you can run any arbitrary logic you need early on. This includes setting one more multiple environment variables. You can key off of one env var, and based off of that set additional variables dynamically if you wish.

Also, other users have done some interesting things with the boot hook