I'm a 3rd year electronics student. I think if you read and asked around you would definitely be able to mess with passive basses and analog pedals by simply playing around with different value components. I know there are books on the net about working on/modifying guitars/amps, but I think they assume you have a certain level of electronics expertise.
As for amps and active basses----Forget about it! Sorry. It's especially a safety issue with amps, as even unplugged the capacitors in amps can store their charge for days (maybe even weeks) and it might be enough to kill you. .1 of an amp can kill you.
Hope this helped.
PS. If you're still young maybe you'd like technical college?