When the role changes it would be nice that the service name was changed, to correctly indicate what it serves. Here is the command line for changing the display name of the service:
sc config AOS50$01 DisplayName= "Dynamics AX Object Server 5.0$01_MyNewPurpose"
This of course doesn't change things like the name of the folder holding the binaries (which you probably shouldn't change if you want to be able to uninstall the service). To change everything you'd need to install a AOS service and possibly uninstall the old service.
Changing the service name is just a quick way to indicate the changed purpose of the service.