[ndnSIM] modification of 'OnInterest' in 'Producer' side

[Amin Karami]

Hi,
I am going to modify some fields in 'OnInterest' in side of the 
'Producer'. e.g., signature of a specific content or freshness field of 
a specific content. I read this page to get more idea 
http://ndnsim.net/doxygen/ndn-producer_8cc_source.html
But i could not understand how is it possible to implement in our scenarios?

I appreciate in advance for any guidance in implementation
Amin