This is my novice understanding, which may be helpful for your even-more-novice understanding, but is likely techically incorrect from the standpoint of someone who actually understands this stuff.
I don’t believe so. I think it just works since its’ in that initializers directory. IIRC, the skeleton includes an initializer with a console.log so that you can see it’s running.
(I think) You only need to run them in a script if you add them in an old-school done-in-the-UX theme component rather than a new school put-the-files-in-the-right-place way of doing things.