TempCpidEnquiry As far as I know the process of changing the IMEI is you go to their website, give them your IMEI and some money and they swap your IMEI with another phone's IMEI. Now this process does not involve handing over their device physically so they only have your IMEI and the changed IMEI.
How could that work? Your phone's IMEI is stored in the phone. How would you imagine that somebody just knowing your phone's IMEI would be able to change it?
I watched a little bit of a randomly-chosen YouTube video. It seemed to me as if maybe the process included enabling adb access from a computer, and then perhaps running an app on the computer to enable some anonymous person to have privileged access to the phone. If so, what would happen after that is unclear. Offhand it's not clear that would be a safe process.
TempCpidEnquiry I am less concerned about the government knowing about this change because IMEI is unique anyways whether it's the genuine one or the replaced one.
I don't understand this part. Again, devices have various behavioral characteristics that differ in detectable ways. If somebody swapped car license plates between a Honda miniMOTO motorcycle and a Tesla Cybertruck, would people be fooled? Would a toll collector at a bridge agreeably charge the Cybertruck a discount toll because it had a license plate from a miniMOTO? Phone models differ in ways that aren't visible to the naked eye, but are visible to a cellular carrier.