Why do you say he changed something in the cookie? The member level is maintained in the database so there is no way he may have changed any info related to him. What may have happened is that the last time he hacked your forum (this is a presumption based on your statement about being hacked again) he got the access data for a moderator and he is using it now. Did you change all admin and mods passwords after you were hacked the first time?
Yes, but did you change the passwords for admins and mods? Otherwise how would he found out the moderator password? Also do you have the IP used by him? Can you post it here?
HooH, I'm not sure your problem is similar to the one covered by that fix. Read the emails I've sent you, specially the last one regarding that specific moderator. Of course, you should apply the fix, nonetheless.