A lot of modding, and I've been guilty of this, is marking the bass as your territory like a tomcat, but I s'pose it is more hygenic to put on a different bridge/set of tuners/pickguard than peeing on it.
In my case both of my Epiphone vintage pro thunderbirds got Gotoh GB650 resolite tuners at around £100 a set. There was nothing wrong with the stock Wilkinsons but I like the aesthetic of the more vintage looking Gotohs.
Yesterday I was writing a list of mods to do on my sunburst vintera mustang bass - I have a black pickguard incoming and I will fit a thumbrest (on the bass side, so not a tug bar), shield the cavities with copper tape, put on a set of Chromes (is this a mod?) and roll the fingerboard edges. I'm not going to change the pickups though as the stock ones are surprisingly good.
I imagine there is a similar urge for people to personalise their gear in a lot of hobbies. At least basses are cheaper and have less depreciation than cars.