Unfortunately Price Rules are not available in my version, that would have solved a lot of problems.

It is the customers VAT number that has the problem with displaying as "TAX Reg No." and I understand the work around would be to create custom fields but then I would have to manually enter the VAT Number every time I created a document for that customer, my work around was to add the VAT Number into their address.

Adding VAT as a line item would be similar to adding discount as a line item (if I understand you correctly) - in both cases this is manually doing something a normal accounting package would do aiutomatically. I would create an item called VAT / DISCOUNT and calculate the figure applicable to the product above and enter into each line. That would be a line for the product, a line for VAT, a line for the dscount. Imagine what my quote looks like when I have 15 products listed.