To do anything like you mention would mean having a very friendly relationship with a licenced engineer
Indeed, and I have that in a few key areas - however most of the work is pretty easy. Most of the "circular" instruments are just four screws and the connector in the back; a monkey can change them. Compared to some of the authorised pilot maintenance items, this job is a piece of cake and very safe.
A few years ago, when I was on G, I looked into what is involved in becoming a LAME. I wonder how hard it is today. The financial benefits are pretty substantial.