I'm using a midi controller with the plugin MIDI2LR which works great the only thing which is not possible is the use of the alt key together with the functions.
As an example the [Alt] masking slider which brings up the black and white screen to select the proper amount of sharpening. According to the creator of the plugin, this is actually an LR bug that this is not possible.
Anyone, who knows a kind of workaround?
Coert van Duijnen
The SDK for plugins doesn't provide any way for a plugin to invoke the functionality you get by holding down Alt / Opt, unfortunately.
And Lightroom ignores the Alt/Opt key when changing values through the API.