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, 17 September 2007
I attack one province with many Naval personalities. The defender controls a courtier at home. During the first battle, after engaging, I use the Naval ability, targeting my Yoritomo Brian at the current battlefield. I play Eastern Hub Port so I announce the "Equip" action that Brian can and must perform. Before choosing targets for the effects of this action, my opponent plays Misdirection and intends to pick the other target. How do we handle the fact that my opponent should target an attachment card from my hand but he can't see my hand because it is face down ?
Thanks for your enlightening help.
[edited for correctness : Misdirection can't change targeting of costs therefore Brian always performs this equipping.]
Chris Fuchs (rules official), 20 September 2007
When targeting is restricted based on its face-up features (such as Force, keyword, title, of card type), a player may not target a card whose face is not revealed to him or her, unless that card has been given such a feature by card or rules effects. [ADDED Sept 20 2007]
Also take note of http://rules.l5r.com/Glossary_I-J#Instead_of
If the new X is negated, or fails to happen for a reason other than negation (“do not” wording, absence of relevant game elements), the old Y doesn’t happen.
What this means is that if your opponent plays Misdirection and does not know what any legal targets in your hand are, his targeting fails to happen, and due to the "instead of" rules, you do not get to target your attachment either.