We noticed that we are able to edit a generic note the next day after the day had been closed. If you edit a note template it is changing it in other patients charts that it was used in.
Check your "user rights" relative to clinical notes to see if changes can be made after the day has been closed. Sounds like you'd like to have the ability to amend, but not change. I believe there is a setting in the user rights for that aspect.
Also, there is a difference between generic notes and default notes. Look in the help section to get a good feel for the clinical notes, how they're used, how to set per provider, how to modify, etc.