The Hackshield sents an AhnPacket to the vindictus server and gets an AhnResponsePacket back. If the server does not get a AhnPacket it simply will close your Connection. That's why you can't remove the Hackshield from the client. You probably would need to emulate all outgoing hackshield packets based on incoming hackshield packets. Except if, NEXON/devcat forgot to implement the "close the connection if player does not send the proper hackshield packets" stuff which is highly unlikely.
It's possible to code a hackshield emulator, but it's not easy to accomplish. You would need to write your own hackshield updater because the hackshield updater is also connected to the client (you have to give the client the right code from the updater so the game starts properly) when this is done you would need to do a lot of packet sniffing or at least find the "OK packet" and its structure. I actually have an old hackshield emulator but it was made for metin2 and they had hackshield not hackshield pro wich means they had no hackshield updater and less packets and its crypted with Enigma.