Amazon RDS unable to execute SET GLOBAL command

I am using Amazon RDS for mysql db. I want to run some SET commands for eg:

SET GLOBAL group_concat_max_len =18446744073709551615

But when I run this command I get this error

ERROR 1227 (42000): Access denied; you need (at least one of) the SUPER privilege(s) for this operation

When I try to add privileges, it does not allow me to add. Any help or inputs?