When editing a guest’s profile, you will find the option to ‘lock’ a profile to Guestfolio. 

When a Profile is set to 'Locked', the personal information associated with this profile will no longer be updated by your PMS, and can only be managed within Guestfolio. 

NOTE: The 'locked' data on the guest’s profile is limited to the information in the profile editing page.
It does not prevent any other updates such as reservations being added to the profile or email being sent.