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.
regarding this: http://www.alderac.com/forum/viewtopic.php?f=59&t=63274
And if the Gunso Chitose i target is already in play attached to a legal personality?
The Good Faith rule only refers to bringings cards into play and as the Gunso is already in playing i'm just changing where it is.
EXCEPTION: In card text, when referring to entering play, attaching, using a trait, or taking an action, "cannot" and "can only" are restrictions on the legality of that thing in the first place, not negation of its effects.
Taken from the Glossary C - "Can not"
They are restrictions on the legality of attaching the card. Utemaro does not allow you to ignore restrictions, only honor requirements. You can not legally attach the card to Utemaro. The effect fails and the Gunso Chitose remains where it is, undisturbed. You still lose the Honor.