There are several threads where peeps have modded their Squiers and SX's. Many have had good to great results. Also, check YouTube for bassists showing off their mods by looking for references to this-or-that pickup or electronics.
There's also been a thread or two for something called a Tonestyler. It's some kind of potentiometer do-hickey. I'm no whiz when it comes to electronics, but the demos I've seen are making me seriously consider one for a parts-bass build project I'm doing.
Aerodyne Club #47
Fender Owner's Club #18
Fender Blacktop Club #13
I felt a great disturbance in Las Vegas…as if thousands of Elvis impersonators cried out and then suddenly left the building.