iptables-restore

I am working on setting up a firewall on a server/router (see 
http://wiki.debian.org/green/Router ).  I have considered several different 
firewall packages, but am more comfortable just running iptables in a shell 
script.

However, iptables scripts usually begin with a flush, and then it takes time to 
add all those rules, plus some possible interruption to traffic meanwhile.  
What about if only a small change has been made?  Does iptables-restore flush 
first, or is it able to just change the rule set as necessary to match?  (And 
is there a term used to describe that feature?)

If iptables-restore does not support that, does anyone know of another tool 
(available the repositories) that I can use that would allow me to write a 
parseable iptables rule set?

Thanks.

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