My personal preference is to stay away from group policy, as changes can not be easily undone.
Alternative ways to manage the Windows firewall status:
WMI
http://blogs.msdn.com/saikodi/archive/2006/02/02/firewall.aspx
CMD
http://www.winhelponline.com/blog/enable-and-disable-windows-firewall-quickly-using-command-line/
If your heart is set on group policy, test out the changes in a realistic test environment (an AD/DHCP/DNS server, one or two clients).