Does merrill lynch refinance 401k loans?

Ask your plan administrator. Whether your plan allows loans at all is written into the specific plan. Its not part of every plan. Some plans will allow multiple loans, other require a loan be paid off before another one can be taken. Some plans might allow a refinance. So we can't answer the question you need to ask the plan admin at your employer.

Note: if you have left employment, you HAVE to pay the loan back or it will be considered a distribution that you have to pay taxes on.