LMS 8 overriding server.prefs?

Dears,

I want to configure the LMS 8 to use my existing MySQL. OS is Debian, 10.5

I make sure to have the LMS service stopped, no processes remaining. I edit the server.prefs to contain the correct lines

dbpassword: slimserver_password
dbsource: dbi:mysql:dbname=slimserver
dbusername: slimserver

I start the server, the server.prefs gets updated and refers back to the SQLite as before. (Keeping the line dbpassword and dbusername...)
Please advise.

Thank you, Marcus