Changing security setting on runtime in EC2

Yes it is allowed to change setting in a group which is attached to a running instance of EC2.

Imagine in comissioning you allowed only 80 and 22 port to an instance , later you decided to open 443 also . You dont have to reboot/reinstall EC2 instance neither need to restart any service on Instance .

What you do is to use Amazon Mgt panel , go to that security group and add one more rule.. simple..

This will effect on runtime and instantanously on the running instance.

see here : http://docs.amazonwebservices.com/AWSEC2/latest/DeveloperGuide/concepts-security.html