I've pimped a couple of basses and got them to my spec - usually a bridge change and pick up change but for a bass which you essentially like then as suggested maybe an outboard preamp would give you the tonal variation you seek. I'm using a Basswitch which is pretty versatile with its EQ options and fx routing. They have a series of single pedal which include classic boosts. Link below and all look for Ed Friedland reviews on you tube. I've no affiliation and there are other great preamps out there. I'm just digging these guys and what they do!
https://www.youtube.com/watch?v=qHdikC4jgqo
http://www.rmi.lu/products