irregula,
acturial assumptions pertain to employee turnover, mortality, retirement dates.
discount rate, compensation growth rate and expected return on plan assets as Management assumptions related to pensions. By adjusting these numbers - discount rate increase, lowering compensation growth rate, increasing expected return on plan assets - all of these will increase earnings (by reducing pension expense).
If company decided to go the other way - reduce discount rate, increase comp. growth rate, or reduce expected return on plan assets - this will have an effect on the PBO component – and change prior period service costs – and that increase would be amortized provided the value went outside of the 10% corridor limit.