I haven't ever renegotiated the credit card balance. I suspect renegotiation only works if you're behind on payments.
Here's what seems to be a reliable article:
Myth No. 4: Debt settlement won’t hurt my credit score.
The truth: Debt settlement can hurt your credit score almost as much as bankruptcy would.
We've managed to clear off some significant debt by up getting a debt consolidation loan at a much lower interest rate, and then making damned sure we didn't accrue any more debt. It was hard as hell.
Step Zero: STOP USING CREDIT CARDS
Step one: Raise your credit score. Get your annual free credit reports. Check anything that's on there. Pay off/settle/contest/get current.
Step two: Debt consolidation loan.
Step three: Pay that sucker down.