If at some point you screw up your iptables, there are actually commands to flush them, so you don't have to reboot. I've actually gotten this question a couple times by now so I thought I'd answer it right here. If you added a rule in error, you might just change the -A parameter to -D in the line you added in error. iptables will find the erroneous line and erase it for you, in case you've got multiple lines looking exactly the same in the chain, it erases the first instance it finds matching your rule. If this is not the wanted behavior you might try to use the -D option as iptables -D INPUT 10 which will erase the 10th rule in the INPUT chain.
There are also instances where you want to flush a whole chain, in this case you might want to run the -F option. For example, iptables -F INPUT will erase the whole INPUT chain, though, this will not change the default policy, so if this is set to DROP you'll block the whole INPUT chain if used as above. To reset the chain policy, do as how you set it to DROP, for example iptables -P INPUT ACCEPT.
I have made a rc.flush-iptables.txt (available as an appendix as well) that will flush and reset your iptables that you might consider using while setting up your rc.firewall.txt file properly. One thing though, if you start mucking around in the mangle table, this script will not erase those, it is rather simple to add the few lines needed to erase those but I have not added those here since the mangle table is not used in my rc.firewall.txt script so far.