Polymorph Can Swap a field Npc or not?

Polymorph
:Swap a fielded Character with a non-Npc Character from that player's used Pile.
if i have a npc character in field, one other character in my used pile.
can i use a fielded npc to swap another character?
:Swap a fielded Character with a non-Npc Character from that player's used Pile.
if i have a npc character in field, one other character in my used pile.
can i use a fielded npc to swap another character?