As you may already know, Microsoft has introduced a feature called First Release on Office 365 to help customers to discover mew services or features before they have been roll out widely to all customers.
If this was a great improvement to be prepare for potential changes, this had a limitation: this applied to all user within your organization
An update is currently rolling out to provide more granularity for the First Release option, letting you to target either your entire organizatoin or only selected user accounts.
If you select the second option – Select people, you will get an additional section to select which users are selected to get the First Release. You have to enter manually the email address or the name to make account appearing
Once this option has been enabled, you will be able to do a bulk update to enable the First Release to more user at a time using a TXT file containing the email address for each user to be added – one email per line
To remove a user from the First Release list, just hit the Pick people link, and then select the user to be removed and choose Remove people