help! reg permission

I have a query regarding when to seek ICAI's permission to do an additional course. I am writing CPT this dec. My situation is that i want to concentrate more on CS and MBL so i just want to clear IPCC both groups with good marks and then think about articleship after i have completed CS program. So i wanted to know whether i should seek permission from ICAI after clearing CPT or after clearing IPCC i.e. during the time of articleship?? I am going to enrol for M.com and CS in a weeks time.