I'm curious about how I might modify say my Aviation Radio (my hand
held spare I keep in case of lost electric in an aircraft). To pick up
amateur bands as well as the Aviation bands.

I'm not interested in the slightest as to whether or not this is
legal, I'm simply looking for educational purposes.
I wanted to get one and then I became curious ... as to how difficult
it would be or how it would be done, what kind of reading I would do
if I wanted to build/modify any radio etc.