It is possible to renew the visa by applying in the prescribed from @ airport Emigration office. the process is known as retrun visa. fees is 500 per head. 6+6 month is possible if the visa is valid or upto the validity of the visa they will sanction by issueing a visa . its a matter of just going to Emigration office at the airport along with the typed appication. better to renew before 6 months from the depart date