DDR Allocation condition waivers

Calendar year 401k plan has a discretionary annual match with a last day allocation condition and DDR waivers, does not have 1000 hour allocation. Client would like to change mid-year to a payroll based match - when we amend the plan to remove the last day and add payroll period (not sure if it is retroactive or prospective) but do we need to protect the DDR waiver group? Technically since last day has not been met nothing has accrued. Thanks!