I'm afraid it's not possible, device Id is in NV: region 41, it contains Nuvi ID, all your maps codes, probably your Nuvi registration date on myGarmin and first satellite fix etc. Everything is in reg 41.
You can find device id in Garmindevice.xml, in Garmin folder, but it is written by NV every time you restart nuvi.
But many features are model related, in some models this can be changed flashing another modded flashable firmware and/or adding them modding region 140.
See [Only registered and activated users can see links. ] and following posts, but Neil wrote:" there's no change to Apps on device".
If you convert a 3790 to 34xx,for example, and enable features, Garmin apps will keep on seeing it as a 3790, but Webupdater and Mapupdater will download 34xx files and Smartphone link works with it.
Conclusion: IMHO the only option is not to change unit id, but convert Nuvi to another Nuvi model, but IMHO not possible and convenient for 3590.
See also: [Only registered and activated users can see links. ]