Using a batch file:

tasklist /FI "IMAGENAME eq isitvMix.EXE" 2>NUL | find /I /N "vMix64.EXE">NUL
if NOT "%ERRORLEVEL%" == "0" start "" "C:\Program Files\Mozilla Firefox\firefox.exe" http://127.0.0.1:8088/api/?Function=OverlayInput3&Input=1

in the Windows scheduler will invoke overlay 3 using Input 1. In my case, input 1 is the video running the Youtube subscribe instructions. I use Firefox, but you can change it to Chrome. It uses the standard Vmix api call. If vMix is not running, nothing will happen. Every time the api is called it leaves open a browser windows with a successful message. I can live with that. It is hard to manage a 1-man production.

For existing presets, you can reorder the inputs by editing the vmix preset file. This will ensure that the correct input always is used. ALWAYS MAKE A COPY OF YOUR PRESET FILE BEFORE EDITING.