Can I add Class after reconciling without messing up bank reconciliation

Yes, you can add Class or changes after reconciling the transactions. As long as the change doesn’t include the date and amount of the reconciled transaction. There is no need to undo bank reconciliation to add Class in QBO.

How to undo bank reconciliation in QuickBooks Online Accountant (QBOA) version?

Undo bank reconciliation feature is not available in any plans at this time. It is available in Accountant version only. In order to UNDO IT,  first log in to your QBOA account Go to Client home page screen Click the company gear (upper right corner) Click Reconcile under Tools Select Bank Account to UNDO reconciliation […]