Eric,
I assume you are talking about your test system; since you would NEVER make such changes in your productive system without first testing the changes, right?
The below method works in many cases.
VA02
Select the item
Remove the plant. Press enter. Press Enter through any warnings.
Replace the plant. Press enter.
Save the order.
If the order item has been delivered, you will have great difficulty in changing anything.
Best Regards,
DB49