You can use it at google sheet by adding "identifier_exists" as a new column and give value as FALSE
You can use feed rules in Google Merchant Center. Choose identifier exists as the target and set it to no
Then also clear brand, mpn and grin attributes.
Here is the documentation: https://support.google.com/merchants/answer/7450276?hl=en
Here is the rule:
When submitting product identifiers the following rule applies.
If a manufacturer has assigned a bar code, then submit brand, mpn (if available), GTIN and set identifier exists to yes.
If the manufacturer has not assigned a bar code, then remove the values brand, mpn, gtin and set identifier exists to no.
Otherwise you get limited by product identifier warnings.
For example in my application, you can import all data, then edit the attributes in the editor, so that you can easily manage everything in one area.
YOu can use feed rules, explained here: https://support.google.com/merchants/answer/7450276?hl=en