Hi Mark,
First, for CC 121, that CC is used by the script to create asynchronous note programming, which is what allows the ability to play harmonized and polyphonic legato with a greatly simplified engine code (simpler engine code is more reliable, robust, and less prone to bugs, and easier to add new features on top of in the future). Without getting into the details, it's an obscure Kontakt trick to enable a software design pattern which is normally impossible in Kontakt scripting.
We didn't anticipate people using the "Reset All Controllers" message and we can find another CC for an undefined purpose. However, there isn't a truly perfect solution, as in every conceivable universe, someone is bound to try and use every CC number for some reason or other. We felt the reserved/defined CC's at the end of the list were of better use than undefined ones that users may frequently map on their controllers, but we can reconsider this, or at the very least, offer users a way to configure the library to choose what CC's it uses.
Secondly, I'm not sure what the confusion is regarding ornaments. Every ornament is freely accessible using the latching (red) keyswitches directly under the playable range. Mousing over each one tells you the name, and additional you can use TACT to convert them to "Tarilonte"-style nonlatching keyswitches or use other rules like velocity to trigger them instead. It is worth noting, if you click on the "VEL" tab in TACT, you will notice a few ornamentations have velocity layers. In Trills, for example, the velocity you play decides the trill interval. In Bend Up, it controls speed.
The weighted probability ornament system is a holdover from the previous Ventus engine. I personally don't really have a use for it, since I prefer to manually choose the articulations I use, but I'm sure some people find it entertaining!