Hi SouthNapan1,
Working with QuickBooks Online means you save tons of time with your business bookkeeping. It's great to hear that you're taking advantage of the bank feed tool to add transactions directly to your QBO account. Depending on your needs, you may need to alter a tax code after matching it in the bank feed register. I'll explain how to do that.
You're on the right track in terms of the steps you'll have to take to adjust the tax associated with your transaction. Once you Add/Match the transaction from the bank feed, you'll navigate to the expense record in QBO to adjust the tax amount.
Click the expense to open it, then click the Sales Tax column to select a different tax code. You'll select from your previously set up taxes, then manually adjust the tax amount below the "Total" on the bottom right-hand side of the expense. Once you do so, click Save.
When attempting to save your changes, QuickBooks Online will prompt you with the following message:

It will be up to an accountant's expertise to decide whether or not to proceed with these changes.
I hope this helps clear things up for you. If you have any other questions, or if you'd like to run this by our tech support team for further assistance, please reach out to them here: Get in touch.
Have a great day.