You're legally (and technically) prohibited from re-programming GPS modules, GSM modules, and probably many stuff in cars as well.
(Actually, maybe contractually when it comes to GPS modules.)
GPS et al would be non-functional if everybody could make a jammer.
(That’s not to say that app stores fall even remotely in that category.)
>GPS et al would be non-functional if everybody could make a jammer.
Then it should be illegal to make a GPS jammer. Making it illegal to reprogram a GPS receiver in any way is unnecessarily broad.
It would be difficult to catch in an inspection if you could reprogram the OEM parts.
I don't care about closed-course cars, though. Do whatever you want to your track/drag car, but cars on the highway should probably have stock software for functional parts.