Just came across this, If its for a specific NPC ..... How about attaching a script to it like this;
Short Counter
Begin OnHit
If (Counter == 0 )
Set Counter to 1
ElseIf (Counter == 1 )
Set Counter to 2
ElseIf (Counter == 2 )
Set Counter to 3
ElseIf (Counter == 3 )
Set Counter to 4
ElseIf (Counter == 4)
UnequipItem Sword
EquipItem Bow
Set Counter to 5
Etc.....
This script means that on the fourth hit, the Npc will trade out weapon types. If you continue to "up" the counter and set 10 to a different weapon type, and then looped the counter back to 0, you could techically have the NPC switching weapons during the entire fight. Hope this helps.