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If you are forced to lower the discount rate then first thing is you generally need to do is add assets via a contribution.

The new amount of assets now has a lower required rate of return but again brings up the decision to take more risk than benchmark (liability) and pursue a higher rate of return or the same risk as benchmark and immunize the portfolio.

Credited rates of an insurance company is an opposite concept but has the same effect on required rates of return. If credited rates are decreased the asset pool doesn't have to produce as high a rate of return to meet the liability. Think of credited rates as a payout of $5 for 5%, $4 per 4% etc per $100. Lowering the credited rates decreases the amount of payout. The payout of a Defined Benefit is defined for perpetuity, you are changing the discount factor for the payments. Insurance credited rates act as an offset to this problem as the rates are variable based on the asset portfolio so a lower expected return on the asset side lowers the credited rates (assuming there is no floor). Generally barring very specific statements. Required return for insurance should be "Earn positive spread to contractual liabilities, commensurate with claims paying ability being paramount" whereas pension has a discount rate that should be followed unless specific provisions allow the company to take more risk.