Shoutbox

Yes you could do some action when a nudge is recieved, but with packet sniffing you can not dismiss or change packets. The packets will still be handled by Messenger and thus Messenger will still shake the convo window and all.

If you don't want to shake your window and make a sound and all that (because it isn't that easy to exactly 100% simulate a decent nudge with a script), but you want a toast to popup or something, it would be much easier because then you could simply globally disable nudging by patching Messenger.

But you can not just disable Messenger from shaking the window and all when it recieves a nudge without patching Messenger. And patching will mean it will be disabled for all contacts.

With a proxy you can pick out individual packets for specific contacts and then dismiss those packets so messenger wont recieve them for those specific contacts.