Place your Pak file here: /Users/[username]/Documents/Larian Studios/Baldur's Gate 3
Open modsettings.lsx with TextEdit. I usually copy another instance of the Gustav strings below the original (from the node id to the closing node <>). This allows me to keep the same formatting.
In the copy you created, replace the Gustav values for the name of the mod, found in the json file under the Folder value. Then replace the UIUD value. You don't need to touch the version value. Save. Take note of the new time stamp of the new mod settings file. Start the game.
If the mod fails to load, look at the time stamp of the mod settings file. If it has changed since your last save, that means there is something wrong with the mod file and the BG3 executable restored the default modsettings file. It might be a question of mod load order, or you might need to install additional mods to run your mod (such as Patch3Mod or ImprovedUI).
I would install the mod myself to test it out for you, but I recently uninstalled the EA version of BG3 from my Mac to avoid any cross-save conflict with my instance of the game on GeForce Now.
It's funny, I went into the documents folder on my mac, and there was an already existing Mods folder in the Baldur's Gate 3 folder, which I never put there myself. Should I just put the Pak file in that?
