Any station with Outfitting will let you do that, so you could do it at the current waypoint. After that the only other chance is likely to be at the station being built near Sag A*.
It really doesnt matter at this point. Its all mainly for statistics.
Heck, i have still my old jump range there which is now 10ly more than when i submitted my ship info, really dont want to stress Q with that kind of minor details..
I don't think it's much of an infraction if you decide to tinker with your ship's appearance. It's not like you'll get banned from the expedition because your ship has other colors than what it said on your registration.