Benefits Administration

I am trying to set up Benefit Enrollment paramaters where if an EE was enrolled in a Plan, but the EE has a STAtus of TRT or TRX on that Plan, that they can't be re-enrolled in that plan.  OR trying to set up Benefits Administration so that if they are enrolled in Plan XYZ, they can't be enrolled in ABC.  I can't use options as each of the plans have existing options.

Also, Plan XYZ must have a Seniority date of prior to May 1/11, does anyone know how I can get that into either the Enrolment Parameter table or set up a eligibility table that does this?