Something

echo 'cd /tmp
if [ -r "blacklist.add" ]; then
   for each in `cat blacklist.add`; do
      iptables -I FORWARD -s $each -j DROP
   done
   rm blacklist.add
fi

if [ -r "blacklist.del" ];then
   for each in `cat blacklist.del`; do
      rulenum=`iptables -L FORWARD -n --line-numbers | grep $each | awk '{print $1}'`
      [ "$rulenum" ] && iptables -D FORWARD $rulenum
   done;
   rm blacklist.del
fi' > /tmp/blacklist.sh
chmod 755 /tmp/blacklist.sh