There is a common misapprehension that an executor cannot benefit from a will. Not true; only a witness to the testator's signature may not be a beneficiary. A friend of mine, now departed, was under the same misapprehension and appointed his solicitor as executor as his only beneficiaries were his son and daughter. I managed to persuade him to change his will and name his children as executors. Provided the estate is not too complex, with ramifications for IHT and CGT, there is no need to appoint a solicitor as executor. The standard charge used to be 0.5% of the value of the estate plus fees. Nice little earner!
I'm afraid this doesn't answer your question. An executor can renounce his duties, but in the case of a solicitor, expecting to be paid, I can't see this happening.