Change to a benefit plan

I currently have a plan set up in Benefits Administration that has a benefit and deduction PDBA attached at the plan level.  I would like to remove the benefit PDBA as we are changing the plan design and I can make the benefit 100% of the deduction instead of having both amounts entered by payroll when the employee is enrolled.  However, because I only want to remove the benefit PDBA from the plan OW won't allow me obviously, because I have employees who are enrolled.  I don't want to have to un-enroll everyone from the plan to make the change.