I was unable to get the crash that you got from your Custom Target Text. However, I did find an error in the plugin getting it to show. So you need to open the Target Core in a text editor, go to line 929 and change it to say:
If you changed it to 1 ally, I can't think off the top of my head how to make the actual selection change between selecting all allies and selecting just one.
You would make the scope of the skill 1 ally then just a slight modification to what I provided to you in my first response:
<Custom Target Eval>
</Custom Target Eval>
That way the player will select one target, and if the actor has state 134 it will end up affecting everyone instead.