XSR125 “Downgrade Tuning”?

Hello people! I think about a suitable moped for my nephew and fell in love with the XSR125. I will buy him the A1 (he will soon be 17), but he still has NO LEEI car experience! I don’t feel good about giving him a moped with a highway speed, but would be happier to give him a Fz, which does not run faster than 55 km/h. So that he can keep up with the city traffic without any problems. Of course you could go the official way via AM (with really pitiful 45km/h), but that means for me completely stupid and unnecessary costs for FS and also for the moped. So A1 would be really useful and desirable. Would I therefore be very pleased to have the moped down to 50…55km/h for a year. Does anyone have an idea where I can do this? P.S.: If this limitation is achieved by a sim plen mechanical intervention (e.g. final stop at the gas train) would of course be all the more welcome to me…