Answer
Yes. If an ArcGIS Online trial organizational subscription is being converted to a full organizational subscription, the same user name can be used to activate the full organizational subscription.
However, to activate a new full organizational subscription or to join a pre-established organizational subscription with the user name that already exists in a trial, the user name must first be deleted from the trial subscription.
Only an administrator can invite, disable, or delete members in an organizational subscription. However, an administrator cannot delete their own user name.
If the desired user name is the only administrator on a trial, the administrator must invite a new user and grant the new user administrative privileges. The new administrator then deletes the original administrator from the trial organizational subscription.
Note:
Prior to deleting the desired user name from the trial, any content owned by the desired user name must be deleted or transferred to a different user so that the desired user name no longer owns any content.