CodeMirror is being used on a saas platform i use daily.
I was wondering if its possible to extend the codemirror editor from the browser?
Possibly, but not easily. The issue is, at least in version 6.x, that you’ll need access to various exports from the packages, and those probably won’t be easily reachable from external code (and importing duplicates of them won’t work either).
But you can get access to the editor object with the .CodeMirror property on the DOM element with class CodeMirror in version 5.x, and using EditorView.findFromDOM in 6.x.