If I vertically drag-copy a note in the PRV down to be a key switch, it doesn't always take effect on that note. Sometimes it does but many times I have to advance the key switch to make sure it activates before the note. This may be normal, l don't know.

Is there a way to insure that these inline key switches get activated first other than manual moving the keys witches?

I have found it is usually necessary to slide the keyswitches a few ticks to ensure the switch hits the VST before the note itself. As far as I know this has to be done manually.

I also position keyswtiches a bit before the notes where the change is to occur. You have to ensure the keyswitch is sent to the VST before the note that needs it.

Thank you for your answers.

 A little CAL script could do this for you: select all in the key switch range and shift back a few ticks.   Or even the "slide" function can do it.    Combined with setting a minimum length, and a 0 velocity ... should have what you need.   It may be superstition, but I always try to have the Note Off of the key switch finished before the Note On of the musical note.