It won't affect previous transactions, accounting171.
QuickBooks doesn't have a retroactive effect so the transactions you created for those items won't be affected. Let me walk through how to change an item from taxable to non-taxable:
You can refer to the Product/Service List report to get a list of your items that have been marked Taxable and Non-taxable. Here's how:
Please let me know if you have other questions. Have a great day!