My QuickQuestItem has the ability to write / update a macro on mouseover but I don't really see the reason for having this?
If you're looking to make 10 macros to automatically be created/updated when you join a BG, that's possible. As for arena, as long as you're out of combat for a moment and have a chance to gather the names it's doable.
From what I can tell you're looking to target the closest enemy to cast a stun.
If this is the case a simple macro for that could be made with this:
Code:
/cleartarget
/targetenemy
/cast spellname