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.
I give my (non-resilient) Personality Resilient through some means (let's use the newly previewed Light of the Morning Sun as an example, spell that gives the guy it's attached to Resilient).
A battle resolution happens, and that guy doesn't die. His attachment dies (through resolution or some other means, whatevs) so he no longer has Resilient.
I give him Resilient again. Does he survive the next battle?
No. Once the Resilient keyword negates a destruction, future new instances won't be negated.
Even if you gain the keyword by different means, or if you lose it for a while and later regain it, the game state remembers that the card has already been "saved" by a use of a Resilient keyword.