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.
Based on an idea and initial code from Stoob.
Download/git clone in your extension folder, enable the extension, or use the native civicrm extension installer.