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.
Can I share Koutetsu Sessou to non Lion clan personality (example : share to Shinjo Xushen) ? (Koutetsu Sessou Armor • Unique This Personality has a minimum Chi of 5. Can only attach to a Lion Clan Personality. This personality has the Tactician keyword. Battle: Move one of the Defender's target Personalities to the current battlefield. If he moved, straighten him and gain 2 Honor.)
based on Comprehensive Rules, Attach: "Transferring a card from one unit to another is not attaching."
Can I share Koutetsu Sessou to non Lion clan personality (example : share to Shinjo Xushen) ? (Koutetsu Sessou Armor • Unique This Personality has a minimum Chi of 5. Can only attach to a Lion Clan Personality. This personality has the Tactician keyword. Battle: Move one of the Defender's target Personalities to the current battlefield. If he moved, straighten him and gain 2 Honor.)
based on Comprehensive Rules, Attach: "Transferring a card from one unit to another is not attaching."
http://rules.l5r.com/Glossary_T#Transfer
Transfer
To take an attachment card from one Personality and add it to the unit of another, different Personality.
A player does not need to pay the card's costs when transferring it, but does need to meet requirements and restrictions of attachment. Nonetheless, the transferred card is not attaching to the new Personality for purposes of things that are triggered by attaching, and is not entering play.
Bolded for emphasis.