When Freddie Mac late last year quietly announced a new mortgage securities designation for pools of loans with sharply lower minimum servicing fees, it looked like a program set up for one of the company’s major seller/servicer clients. Mortgage lenders of all sizes have wrestled with earnings volatility as a result of having to take impairment costs and earlier-than-expected amortization expenses as the value of the mortgage servicing rights drops when refinance activity spikes higher.…