altering existing security group

hi,
I am creating sec group (lets call it A_SEC) using ec2_group and this works fine. I need (later) to change existing sec group (B_SEC) and add rules to grant access to whatever is using A_SEC.

I cannot do this using ec2_group as it complains about missing description. can anybody guide me how to do this. or maybe I should write my own module. are there any plans for ec2_group_roles?

thanks