Another option is to run a command in node-red, this means it will only run after openplotter & signalk have booted up & if you change to a new installation it will be inside the node-red flows backup. The inject node can be set to run once at startup which will then trigger the exec node.
Image below is a python 3 file with containing just "print("test worked")"
Image below is a python 3 file with containing just "print("test worked")"