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 April 2008
If instances of "can not" in Effect text on cards mean negation, do instances of "can" without "not" mean the negation of negation, as they imply allowance?
This isn't frivolous, it hearkens back to the Unopposed/Opposed issue, where simple grammatical restructuring/miss-type created an entirely new card meaning. As Can appears in effect text, it must have some defined rules meaning. At the moment, I believe Assigning Blame is the only card in which "can" appears in a permissive form in effect text, and that needs to be nailed down to prevent future confusion/interpretation.
A player, 3 April 2008
If instances of "can not" in Effect text on cards mean negation, do instances of "can" without "not" mean the negation of negation, as they imply allowance?
No, instances of "can" alone do not mean negation of negation: they override specifical rules, per Glossary, Can.
Text that says something “can” happen overrides any rules mentioned in the text that prohibiting that thing from happening; [...] "Can" does not break rules that it doesn't specifically refer to; [...] Likewise, "can" does not overcome restrictions or negations from card sources, unless overcoming such things is specifically mentioned.
For example Hiruma Aya's Recon Limited action overrides the rule that states only Cavalry units can assign during Cavalry Maneuvers but it doesn't overcome the rule that states units led by bowed Personalities can not normally assign; Soul of the Winds overrides the rule that states a Ranged Attack can only target a Follower or a Personality without Followers, but it doesn't overcome the part of the same rule that states this target must be in the current enemy army.
Context matters. Indeed they sometimes grant an additional time an ability or trait can be used in a period of time (see Glossary, Additional, §3). For example Doji Masako's Reaction lets you use one of your abilities not on a card an additional time during the turn it was used.