You can use any word you like, Mary. I would recommend sticking with what you have been using. Alana and I use different words as our search cues. I believe her word is German for search or find it. Mine is Italian for find it. No particular reason except to chose a word not used in our everyday language and one that didn’t sound like other verbal cues we use for various behaviors.
I think it is a good for you to intentionally strengthen the word association, yes. However, I don’t think you need to do more than be conscious of using it during training…especially during the reward. The reason being that you don’t want her to think that simply nose targeting a scent tin you presented is the final behavior.
What you can do is build into the reward period a few nose targets. Send her to search as usual and reward as usual. While you are still at the source rewarding, ask for a few nose targets (using your word) for even more treats. This will help to prolong your reward period (which you will need for actual truffle hunting) and it will also keep her engaged during the time that you will be down on the ground with her digging and searching for the truffle.