If you mean, how can one add something like custom MIDI modifiers, then I think this is done with the VST Module Architecture SDK. I think this is also how Step Designer is implemented.
Ah, sorry – yes, I think the MA SDK targets only Cubendo.
Perhaps Steinberg will add this in a future release? It would be a cool feature. I note that there was an extensive expansion of the MIDI scripting capabilities in Kontakt 5.
The “Drum Player” MIDI Mod, used by the “B-Box” presets.
(I didn’t have H5 handy, and couldn’t remember the title of the actual MIDI Mod! )
I think the answer is no for both. I think you have to license with Steinberg to create libraries that have Macro pages. And as far as I know there is no Halion SDK where you could make a plugin for it. I know we’ve requested stuff like that.
The Steinberg/Yamaha policy is unknown at the moment. I can’t understand why it can’t be allowed to create content for HSSE/HS2. Maybe the Japanese can talk sense to the Germans?