I can't say that I understand quite what you're asking. Can you give a reference to wherever you read about this, or to an article or tutorial that describes "iptables rule spoofing"?
To my understanding, if you want to 'spoof' an iptables rule, you'd need to make a new, identical rule
which would act like the original rule, thereby 'spoofing' it.
Does this make sense?
Sasha