Sales Ledger account option - allow Use VAT Codes as SOP default to be available for Country Codes other than GB

The Sales Ledger Account option Use VAT Codes as SOP Default is currently unavailable (greyed out) for an Irish customer account (Country Code IE) which is not VAT registered, so it is using VAT Code 1. When entering SOP Sales Orders, most transaction lines are ok as they relate to standard VAT rate Stock items, but there are occasions when some Stock Items (eg. childrens clothing) which are set up as zero VAT, actually pick up the VAT Code 1 from the customer account (which is set to VAT Code 1, but the Use VAT codes as SOP default is greyed out).A customer would like to be able to amend this option so that it is unticked, but keep the accounts Country Code as IE, with a VAT Code 1 (Standard 20%). The SOP Order Entry program may also need to be amended?