I was wondering if there was a way to lock a record (allow no more changes) via script or checkbox? We have quotes and invoices which are editable by permission, but once the record is closed, we want to not allow any changes to be made (except by master password).

You need a field that you can flag in the record such as lockrecord (number).

Create a privilege set. Under the Records section of defining the priv set, choose Custom privs...

Go to the table that you want to control and under 'Edit' choose Limited.

Then the calc could be:

Case ( lockrecord; 1 )