use /haltdef on these events (beginning with a ^): ACTION, BAN, CHAT, DEHELP, DEOP, DEVOICE, HELP, INVITE, JOIN, KICK, MODE, NICK, NOTICE, OP, OPEN, PART, PING, TEXT, UNBAN, USERMODE, VOICE, QUIT, SERV, SERVERMODE, SNOTICE, TOPIC, WALLOPS and replace them with your customized text.
For ex:
on ^*:JOIN:#:echo $chan $nick has joined $chan | haltdef