Q. Can anyone edit a note?
A. Anyone can edit/delete their own notes (no ACL)
Q. Can note visibility be changed?
A. There is an ACL to allow users to set note visibility
Settings - CRM - Note Visibility
Q. Can you override the Note Visibility?
A. There is an override for note visibility (Timeline entry ACL)
The user must have the edit/delete Timeline entry ACL to be able to edit or delete anyone else's notes
Important Notes are not treated any differently than regular ones