I spoke too soon and my answer was not correct. Apologies, let me set this straight:
Both changing an existing role mapping and introducing a new role mapping could potentially trigger a clear of the respective realm cache. This is true for realms like PKI, LDAP, AD etc.
Now, with SSO realms like SAML and OpenID Connect we can't do this as we don't use the cache because of how the SSO flow happens and this is why your changes are not reflected. Calling the _clear_cache API will also have no effect for OpenID Connect, you would need to logout via Kibana and log in again.