To disable the script: /disable #displaytext
To enable the script: /enable #displaytext

You can override your own text being formatted by pressing ctrl+enter instead of enter.
It doesn't format your text when you paste something.

If you only want to change other people's sentences, and not yours, then you can just delete the on input event entirely, leaving only the one line of code.

Code:
#displaytext on
on *:input:*:{ 
  if (!$istok(/ $readini($mircini,text,commandchar),$left($1,1),32)) && ($istok(channel chat query,$window($active).type,32)) && (!$ctrlenter) && (!$inpaste) { 
    haltdef 
    .msg $active $1- 
    echo -artc own $+(::,$me,::) $1- 
  } 
}

on ^*:text:*:*: haltdef | echo -mbflirt $iif($chan,$chan,$nick) $+(::,$nick,::) $1- 
#displaytext end

Gone.