Hi vintagevibe,
You can’t create an expression map by “Import keyswitches from instrument” because there are no keyswitches to import.
Usually when you have an instrument with keyswitches all the articulations are loaded with the instrument and it works like “solo” and “mute” for the midi events.
But Studio Strings is slightly different. There is only one articulation (preset) loaded at a time. When you select a different articulation from the preset selector it removes the currently loaded layer and loads a new one. This might be too slow to be used in real time as a keyswitch. This is probably reason why it was made not automatable.
But you can still create an expression map. Load HS as instrument track. Load the articulations you want into different slots.
Set up the expression map so that instead of sending a keyswitch note on message to the instrument it will change the midi channel on which the midi data is sent.
This way you will have one track in project window, you can trigger the articulations from midi keyboard or draw them in the midi editor.