I don't know if some1 already posted this, but anyway.
I tried hlapex on a server l2ia (c3 off) and if i turned on hlapex, i coudn't login. So i logged, in i pressed "Agree", and on server select i turned hlapex on. U must w8 5 secs before entering the server, so that hlapex will "inject". Then, you enter the server and you can use hlapex.

I think the file that looks if you have hlapex turned on, is a specific file in GameGuard folder, but it looks only on login
That's from me, if it works on other servers, post results.