Two Business roles to change alternately, is it feasible?

Hi,

     I have a requirement where i hv to create one business role (zaccountant1) by copying existing role(zaccountant) with few changes. Now, client want that the new role should be assigned during mid month and month end (eg on 15th & 16th Jan then on 30th 31st Jan). rest of the days Zaccountant role should work.day

Role     Zaccountant1- for mid and month end

           Zaccountant - rest 27 days of the month.

  Is it possible to change the role automatically, so that we need not to assign it again and again?? possible?

Please share your views and possibility.

Regards,

Himanshu