Hi @Victor4, I agree with @Bastien_Siebman. There’s not much documentation about this specifically at Asana Developers - API, Documentation & Community Support • Asana about DOM changes and you’d want to be as careful/defensive as possible to stave off breakage as much as possible.
I haven’t looked closely at the code, but perhaps @ShunS’s Asana Navigator: Unofficial efficiency browser extension to enhance navigation for Asana tasks is an example for you. This is a Chrome Extension, so that limits you to Chrome Desktop (and Opera I think). See his GitHub - ShunSakurai/asana-navigator: Unofficial Google Chrome and Firefox extension to enhance navigation for Asana and the readme there.
Hope that might help a bit,
Larry