The question you ask is not just about OpenVix and BH: it's one of the differences between open projects, like OpenVix but also OpenBlackHole and all the other open images, and the vuplus code-based images, like BH and VTi: the complete keys customization is typical of open images.
Under BH you can use some plugins, like SetupQuickButton, but you won't never have the same degree of freedom over the key assignment.