Hi there cdza,
Making sure your transactions have the right tax is important so that your filings are correct. QuickBooks Online is a great tool that can keep track of the amount of tax owed to make the process of filing to the government easier. I can provide some information on editing the transactions.
When editing the tax amount on a transaction that is a part of a previous filing, the difference in the tax amount will affect your next filing in the form of an exception in a previous filing. You'll be able to see an exception on each line it's supposed to affect in your filing.
The error message you are shown is to show you that if the total amount of the transaction is different from the original amount, It will have an effect on your bank reconcile. In this case, since you're only adjusting the amount of tax of the transaction and not the total amount, it shouldn't affect your reconcile so you'd be able to say that you are sure you want to complete the edit.
If you have any other questions, feel free to reach out here.
