CiviCRM noverwrite extension
Prevent users from overwriting their record while trying to add a new participant / contribution / membership.
CiviCRM by default pre-selects your own contact details when you register to an event (or other public visible forms) if you are logged in. It is generally a good thing, but might lead to errors, for instance when a team member will overwrite their own contact record, or if a person forwards an invitation they received to someone else. This extension makes the first and last name fields read only, to prevent these mistakes.