I can change ringtones in iOS today. Unless there is some other requirement.
Maybe you want some UNIQUE ringtone? If so, create it then use it.
I know of an application that can change the ringtone constantly when a call comes in. But I don't know what that name is, do you know the application that can tell me the name?
(I am using Iphone X 256gb, Ios 13)
Thanks in advance!