"Beta" here means that you have to use the /beta Graph API endpoints, much like in the examples in the article above. If you need to make changes to the default behavior, simply use the /beta endpoint, no other steps are needed to gain access to the feature.
That said, this only applies to LOB apps that specifically use the mail claim to authenticate the user, which is not a common scenario. Moreover, you cannot control this behavior on third-party apps (or any built-in one), so you should only ever concert yourself with this if you know your organization is creating LOB apps that leverage said claim.