General - Help with C+ programming

okay so here is the proposal
the filter below is designed to work within ettercap
if the programme finds the word "secret" within a network packet it will drop/kill that packet
i am looking to advance this filter so that instead of dropping the packet the filter/ettercap will replace the word "secret" with another word like "hidden"
the filter needs to work with windows live messenger traffic only so i think port 443 for windows live messenger ... not sure??

=example filter=

# drop any packet containing "secret"
if (search(DECODED.data, "secret")) {
msg("forbidden word detected...\n");
drop( );
kill( );
}

any help/advice will be greatly appreciated

The thing you would have to do is to make the program listen on the port. But i don't know if it will work because normaly you can't listen more than on at a time... you must nearly replace the process running on that port...