@d-healey Thanks, simultaneously I just found this thread:
https://forum.hise.audio/topic/9830/attaching-text-json-files-to-the-compiled-binary/6
I really assumed that I could load data like this but that's ok - I will do the suggestion in there of checking for a file and falling back to a default object if not found, at least for the resets/presets code. The main data I can definitely move to a .js no problem. The main data of my entire script including samplers came from a JSON file and I was tricked into thinking it was working fine because the samplers are created at compile with the correct data, and so I figure the UI was as well. No wonder absolutely nothing has been working correctly.