We see on their site:
The C. Bechstein Digital Grand for Native Instrument’s KONTAKT and KONTAKT-Player follows the high standards we set for our acoustical instrument´s development and production: sound and manufacturing at the highest level, made for connoisseurs and people with passion.
Then it is ok with the free KONTAKT-Player.
KONTAKT-Player will have access to every knob defined by the library. Usually, entering the library with the full Kontakt is not needed. (It can be used to add modulators or somethink like this. This kind of use would be more likely with synth sounds). Note that most commercial libraies have their scripts locked, then even with the full Kontakt, you won't be able to tweak everythink.
With Kontakt Player, you are limited by the filter which are selectioned by the library maker, (reverb for example). But I woudn't buy Kontakt full only to add filters (a DAW can do it).