Code:
ON *:TEXT:*:#: {
echo $chan $+($iif(%npre, $v1,<),$left($nick($chan,$nick).pnick,1),$nick,$iif(%npos, $v1, >)
haltdef
}

alias prepost {
set %npre $1
set %npos $2
}

Ok so this should do the trick!
Do /prepost prefix postfix
Example: prefix is <
postfix is >
Now you can change it to whatever you want.
If you don't change it it will remain < and >
Let me know if you need anything else!