GM 8.1 did this; if you had a script of the same name and argument count as a built-in GML function, you can actually override it. This allows use to reimplement features using external_define/call/free and call dll's to override existing features how we prefer to have them implemented in ways that normally end up as rejected pull requests for one reason or another. GameMaker Studio also can do this similar with extension functions using the visual extension editor in the resource tree, but the dropped the ability to do this with ordinary gml scripts and only allow it with external libraries.
I wanted to do this in particular with our dialog functions so if someone wants to get further updates to our widget systems, I wont have to create pr's for anything in enigma concerning that apart from fixing breakages. This will lessen the pr's you guys will get from me concerning dialogs and other features you guys dont care for all that much. People could download and import my gml scripts and compile my dll's from source for their desired OS and wammo they can access my shit without me making a custom fork of enigma that I will constantly have to resolve conflicts with and keep up to date.