You can change your CID indeed but you need S-OFF for that. That will cost you 25 dollars via "sunshine"
But i will give you my opinion since you going to give it to relatives. Keep the 25 dollars in your pocket, flash maximus oreo rom (which is ...
The following two commands worked on Fire HD8 (7th Gen) with OS 184.108.40.206. It should work for Fire HD10 with OS 220.127.116.11 :
pm uninstall -k --user 0 com.amazon.device.software.ota
pm uninstall -k --user 0 com.amazon.kindle.otter.oobe.forced.ota