first of all all ca’s have right to put CA as prefix.
there is no compulsion.
 
they can use other prefix also, it is clarified by icai they can use Dr — so they can write Dr CA or CA Dr …. so we can conclude CA CS is also allowed as Dr is allowed…. so there is no restriction with respect to prefix
there are restrictions with respect to “Designation” which we write below name or on side which shows profession of person