How to map note velocity to plugin parameter (for ALL keyboard notes)
There are few plugins that accept as input a MIDI message for parameter automation.
Generally, you have to set the parameters through the control interface (VST, AU, ...).
You must use the CTRL-middle_click "Operate Controller now" function as indicated in https://community.ardour.org/generic_midi_control
It only works with MIDI events. If only OSC is enabled then the function is disabled.
In any case, "Operate Controller now" allows you to set up a simple and non-shared control.
Probably you can define a more sophisticated behavior within the Ardour configuration files.
Are the specifications for low-level file configuration documented?