Once a sharing rule has been created to share Account records with Public Group A with read/write access to the shared accounts, then this sharing rule can be modified to share the Account records with Public Group B with read-only access.
A field marked as 'Required' on an object (while creating the field itself on the object by checking the checkbox for ‘Required – Always require a value in this field in order to save a record’) can be overridden to make this field 'Read-Only' by checking the ‘Read-Only’ checkbox on the page layout.
Which field type is not available while creating a new custom field in a newly created custom object?