Today I did the following to my Jazzmaster:
My pickup covers are now "aged". Not sure if I'm into it yet, but I'm going to order some aged knobs and switch tips and see how it looks when everything's consistent. Most people like vintage-ized guitars, even if they're new. I kinda don't, but I'll sleep on it for a while and decide how I feel later.
I did it because I changed my pickups to Seymour Duncan Antiquity II's a while back, which are designed to mimic the vintage sound. They're a big improvement over my original Japanese pickups, which aren't like real Jazzmaster pickups at all. But the problem is American pickups don't fit Japanese pickup covers. I filed my original covers a little so these pickups would fit, but they looked kind of weird afterwards... so I thought I'd try this. The only American covers you can get are this color - Fender USA only sells cream-colored covers on their "vintage reissues", even though the originals came with plain white!
Anyway, I'm working on a comprehensive list of upgrades I'd recommend for your CIJ Jazzmaster, along with any caveats like this. I get a lot of traffic from people searching for CIJ Jazzmaster info, so hopefully it'll help. Watch for it soon.
Update: I put my pickup covers back the way they were. I tried all "aged" stuff and it just looked fake. Plain white looks a lot better. (Trust me.)