My condolences for your loss. Normally, the plan is the only vehicle for defining both the benefit and any (potential) beneficiary. For example, most plans, if no beneficiary is specified, will include a sequence of others to define a beneficiary (such as: first children, then parents, then siblings, etc). This may not apply in your case.
If you have not done so, ask the Plan Administrator (which might be contacted thru the HR department of the company) to explain the beneficiary situation to you. To my ear, having a "friend" defined as the beneficiary is very unusual, so there might be more relevant facts.
I'm unsure about your phrase "override the beneficiary", but an estate lawyer may tell you that would be possible only if you can prove fraud or some other incorrect application of the plan rules. At least for me, it's not obvious whether you would have any standing to submit a DRO. BTW, the lawyer may also tell you that the "estate bills" are the responsibility of the estate, not you. (I'm not a lawyer.)