No John, that doesn't do it.  That's because the line items that are on the bill are added from a "billable expense" item on the right side--they are NOT individual product or service lines that can be added to the creditm memo. They include both the billable expense (say $100) and the "markup" say $50.   I can type these in the description on the credit memo, but then the customer will see the line items "Expense" and "Markup" on the credit memo.  Net, doesn't mirror the original bill.  Also, lets assume this is the only transaction we have. If I just add those together and put down a credit for "Expense- $150", then the "Expense" line item on the p/l will say -$50 because only $100 was charged there, and the markup line will still say $50.

PLEASE...truly research this and try before posting an answer.