Hi. Can I know the environment you developed this for? What OS, what version of HackShield, and what version of Mabinogi you developed this for?
Your method of bypassing is pretty interesting since I didn't think of it and didn't expect it would work so I would like to look into getting it to work and personally confirm that your idea works. Given the quality of the program, I assume you did confirm that your idea works so I figure that it's something on my end rather than you jumping the gun and releasing something that doesn't work. You did check that you can log into the game before releasing this, right?
I tested this on Windows XP 32-bit on the current version of NA Mabinogi with HackShield updated to the current version. While I was able to confirm the multiclienting part and that it does get around the EagleNT restrictions, it gives an auth error when I try to log in. I looked at your code and you just make it skip everything but the auth function so I assume you deal with the checks that would normally make the auth function choke when calling it without running the init functions in your HSLaunch program.
Also, I'm interested if you came from another modding community since it's not often I see capable people pop out from nowhere.