Override DBA Begin Date in the Enrollment with Eligibility

We are rolling out some new benefit plans for a group of employees. The eligibility is set as 3 months from the start date for all new employees in that group (I based the eligibility on the DST in EE Master), but all existing employees, the benefits are effective immediately (and the start date for the existing employees is less than 3 month).

Is there a way to override the eligibility date in the enrollment with eligibility to have DBAs to start calculating immediately for certain employees?