the eInvoice workflow module

We purchased the eInvoice workflow module.  We have partnered with Pagero to have supplier invoices electronically created.   In our set up discussions, the "External Supplier Invoice tax Code" form will only pick up tax codes that are set up as "VAT" tax type.  We have forever used tax codes with a tax type of Sales Tax or Use Tax for our Canadian and US companies.  Only our UK company is set up as VAT.   Although at the company level we are Sales Tax, it seems IFS allows us to change the tax type of an existing tax code to "VAT".   

Are we able to do this?   Even though we have history with these tax codes or is it better to create new ones?   Please advise the repercussions of changing this tax type and/or creating new ones.  We are not certain what is the best practice in this case. Thank you