1. This is pretty simple to do. It is really a basic concept within Kontakt. If you have a look at this video: How to Creat a Kontakt instrument
the link should skip ahead to 6:46 where he shows how samples and velocities are mapped. The samples for your instrument are already mapped, so you just need to drag a few velocity cutoffs up.
2. As far as sharing… well, it is so easy, it may not be worth putting the pianobook team through the hassle of creating a new instrument page just for that.