That worked! Thanks!
To be able to use 2 accounts:
I created (but not enabled) a secondary service file, calling it scs-z.service. In this file I specifically point to a different key file of the 2nd Spotify account. Now I can do sudo service stop scs.service and sudo service start scs-z.service to switch.
So in my secondary scs-z.service file I use:
ExecStart=/home/osmc/spotify-connect-web.sh --key /home/osmc/spotify-connect-web-chroot/usr/src/app/rud/spotify_appkey.key --username [user]--password [pw[ --bitrate 320 --name [name]
And by not doing systemctl enable scs-z.service, this will not start at boot (since that would conflict with scs.service).
I am sure it is very easy to write a script that would check which of the 2 services is running, stop the running service and start the other service, to easily switch between accounts…
BTW on the Spotify dev page it says:
Important! LibSpotify and CocoaLibSpotify are no longer under
active development on any platform and are considered deprecated. If you
are building applications for iOS or Android, please use the iOS SDK or Android SDK, and we will be providing a new library for other platforms later this year.
Hopefully this solution will work untill Spotify provides us with an even better solution…