Exemption of GST on car parts on customers invoice

I have a customer that has dropped off a DECLARATION FOR AN EXEMPTION OF GST ON A CAR OR CAR PARTS - DISABLED VETERANS.  It is only for: 

Where the parts are incidental to the labour component, neither the parts nor the labour are GST-Free.

BUT – if a mechanic/service centre supplies parts with a significant value, (e.g. tyres, battery, radiator, muffler & exhaust pipe) during a service or repair with labour being ancillary or incidental to the parts component, both parts and labour are GST-Free (the ATO requires only the parts to be listed on their declaration).

When I am doing the invoice for the customber, I have changed the tax from GST to FRE but my price doesn't change.  Is there a way that MYOB can take the 10% GST charge off the parts and labour when I change it form GST to FRE on the invoice?   But also some parts and labour for the customer's invoice will have GST.

Or should I open a new PRODUCT CODES for only the parts that are only examption of GST and should I open a new LABOUR CODE for Customers that get Labour free of GST?