Microsoft recently released the feature that enables users to self-select which M365 Apps for Enterprise update channel they will use, right within the Office suite apps.
In the February release of the Office 365 Group Policy template files, they have included a new config setting that allows end-users to select the Office Update channel they use. You can download the admx files from here
Creating the Policy
To centrally enable this, you will need to use a Group Policy Object if your machines are connected to Active Directory.
After loading the ADMX templates into Group Policy management, you will find the ability to enable self-selection either for the Computer Configuration, or User Configuration under Administrative Templates/Microsoft Office 2016/Miscellaneous as Show the option for the Office Update Channel experience:
If you are not using Group Policy Objects, or your users and devices are not connected to Active Directory, there is only one other option right now, and that is to use Registry Keys to control this. I think that in the near future Microsoft will bring this feature to Intune Managed Devices or the Office Config Scripts portal.
Registry keys to import are here, which you can save to a .reg file and then import into your registry, of course at your own risk
Windows Registry Editor Version 5.00
End User Experience
Once the policy or registry changes have been applied, the end-users can now self-govern how they receive the Office updates. To do this, they will need to go into an Office 365 desktop app > Click on Office Account and then click on the newly displayed Update Channel setting
Users can now see the options that the Administrator has configured in the Group Policy or Reg files