Please use the word
Identifiers for these
(Yes I see the Label in the MDE. Not sure when it changed. The balloon help still says identifiers.)
Calibre has an internal {id} (used in many places via the CLI), and using Id could lead to confusion) FWIW ID is the number in (##) that is the title folder, if you peeked under the skirts.
You can edit the value, list in identifiers.
You could delete a whole family using the Tag Browser. eg barnsnoble 7
Simply right click on that
elete barnsnoble:Yes
You can add any identifier you want. I added PG:<pg#>
Identifiers have 2 parts
Familyname : value