Thanks but this is not what I am asking you how to do.

I have billable expenses already in invoices.  I need to update the category of the expense in the invoices.  I already updated the category in the bills, I didn't think those updates come through to the invoice.  So now when I get a payment it is crediting a different category than the one on the bill because I updated the bill category.  How can I adjust the category for these billable expenses on the invoice side.