How do de-register extensions for files?

I’m working on a plugin to allow users to register views to file extensions in a modular manner. I’ve found this function:

To register extensions, but I need to figure out how to de-register extensions when a user changes their settings. Is this possible using a different function or null parameter of some think? Or is it append only?

I found t by decompiling the api myself. and have made a plugins with an example here:

how did you “decompile the api”? Interested in this.

Decompile isn’t probably the right technical term; but you can look at the code being run in real time on the desktop version of the app using the inspection panel (ctrl + shift + i [on windows]) and you can step though the lines of code.
It’s all ‘minified’ so it’s not super human-readable but if youre as persistent as me you can figure out what it’s renamed stuff to and try to associate that with the public side of the docs and api.