Lock Tax Status if from Customer - System Option

>Utilities>System Options>Order Entry>Order Entry 

Category Authorization

Type- Can be Global, Assigned or User

This allows locking the Tax Status field after the information is imported from the customer file and does not have to be saved first.  This ensures that the tax status as recorded in the customer file is followed. However, the principle from above still applies, if there is no password set, anyone who has access to this screen may unlock the Tax Status and make changes