If you are logged into the account before the cheat is detected then, yes you can still use it untill the client is closed. X-trap does not update in real time as of now, so that means you would manually have to update x-trap by relaunching the game subsequently your client has been updated to the latest blacklist database.
Source(s)
Myself
I have tried this back in 2011 in my cheating years, as long as the machine is not powered off the hack will remain undetected. Please do not use this information to cheat, I was just simply answering your question.
*I do not know if this still works as I am a legitimate player, and i hope neither will you.