Hi there, ekramber.

Welcome and thank you for posting your concern here in QuickBooks Community. I appreciate you for sharing detailed information about your concern. I'll share steps to ensure you're able to disable the automatic price change once and invoice is done.

To stop the automatic price change, you'll have to turn off or deselect the settings of the Advanced Pricing in QuickBooks Desktop. Please note that when you turn off this feature, you'll also disabling the pricing rule. That being said, it will affect all the sales orders associated with it. Before disabling this feature, you'll want to ensure there are no other transactions linked with the rule to avoid any issues.

Here's how to turn off or deselect the Advanced Pricing:

1. From the QuickBooks Edit menu, select Preferences.
2. Choose Sales & Customers in the left panel. Then, go to the Company Preferences tab.
3. From the Custom Pricing section, deselect Enable Advanced Pricing.
4. Hit OK.

For additional information, you can click this article: Use Advanced Pricing.

Please refer to this article to see steps on how you can make any changes to your items and different pieces of information on how items work in your QuickBooks Desktop: Add, edit, and delete items.

Please let me know how it goes or if I can be of additional assistance. I'll be here should you have any follow-up questions. Have a great rest of the day!