Would PAD eventually have an Advanced Editor like in Power Query for Excel?
It's meant as a Low Code tool, so no, you currently can't edit the underlying Robin code. If you need better Excel handling, use cloud flows.
EDIT: You could copy/paste Robin language code between an editor and PAD:
How do you get access to the Robin language code in PAD?
Create a flow, add some actions, then Ctrl+A, Ctrl+C, paste in a text editor, modify, copy/paste back into PAD