A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 2 February 2010
Can the Battle/Open action from Eighth Legion be performed while the Follower is already in play? It appears that the attachment of the follower is not a prerequisite to return the follower to hand at end of turn. Would using it's Battle/Open action while already in play skip over the attachment part and return the follower to the controller's hand at the end of the turn?
Battle/Open: Attach this card from your hand to your target Personality. Before this turn ends, if this card is in play, you may put it in your hand.
Zen Faulkes (rules official), 2 February 2010
Can the Battle/Open action from Eighth Legion be performed while the Follower is already in play?
No.
http://rules.l5r.com/CE_Abilities_and_a ... Faith_Rule: "If the action involves putting one or more cards into play as a non-optional effect, the player must be able to bring those cards into play legally to meet the Good Faith rule."