Adjust Valuation Results by Arbitrary Amounts
The valuation basis setup screen has a section in which adjustments to liabilities can be entered. A blank entry implies no adjustment:


The adjustments work by multiplying all numbers emanating from the member records by the factor before processing for valuation purposes. It will include member contributions, salaries, lump sum payments and pension payments. The adjustment applied is based on the status of the member at the effective date of the valuation.
If you need to manipulate the liability without altering other aspects of the projected cash flows it is probably better to make an arbitrary adjustment to discount rates (which can be done differently for each member status).