Change GL account segment on Tax line using SLA

Hi,

We currently have 2 VAT codes configured in AP. One of the codes is a 14% VAT code which is our standard VAT percentage in South Africa.

My client wants the GL account of the tax line to match the type of expense on the AP invoice, but obviously the VAT code has 1 defined GL account. They have 34 different types of expenses like stationery, printing, advertising etc.

Is it possible using SLA to look at the associted expense account of a tax line, then look at a mapping of expenses account = VAT Account and change it on the tax line? Can a custom source be used?