In general, a plan sponsor should be able to vary contributions as if they had amended the plan to state what they want to do, without actually amending the plan. But the plan sponsor can't do what is otherwise prohibited. For example, the plan sponsor might feel that only those with service greater than 3 years should share in a given year's contributions. Even if it passes all the discrimination tests because the only participants are NHCE's, the IRS will disqualify the plan.