It's no harder to change than using any other identity provider. If you want to change, the service just needs to provide some way for you to link your existing

It's no harder to change than using any other identity provider. If you want to change, the service just needs to provide some way for you to link your existing account to a new sign-in mechanism. Classically, this is done merely by detecting that you've signed in on two different mechanisms using the same email address. That can still be done with Sign In With Apple for users that have opted to give the service their email address, but for users that opted to use Apple's email redirector, the service will simply need a way for the user to explicitly link it to another account (or to manually provide their email address).