To make changes to the gui-lib package, will I need to clone the whole racket repository and rebuild racket using the instructions at https://docs.racket-lang.org/racket-build-guide/contribute.html or can I get by with just a raco pkg update --clone for the gui-lib package. I’m currently running racket from an installer and not a source tree.

You will need to do the steps described here first: https://github.com/racket/racket/pull/3991/files

Thank you very much! The clarification you linked makes it much clearer what I need to do.

I assume raco pkg update --catalog ‹_pkg-name_› will still restore the original package following these instructions?

yes, although i would probably just switch back to the main branch