[NTG-context] Overriding / redefining / disabling standard commands

List, What is the preferred way to override a standard command? My use case is that I am trying to produce html (and epub, but that has a long long way to go) from the same source I use for pdf. Some features are not needed, and I have separate environment files for each output format to accommodate the differences. I would like to override the standard \index command in one of those environment files, eliminating the generation of index references. There may be other constructs as well that would benefit from this simplification while allowing a common content source file. On a related note, does anyone have a css file that handles block quotations, margin notes, and cross references? I would love to steal bits of it. -- Rik