You could export your events from one calendar using an ical export menu item and the import in the frontend into the other calendar.
Thanks Geraint.
The root cause has been the possiblity to choose calendar when creating an event which made it a bit messy and is why I want to change to only one calendar.
Am I correct that I can't limit the export from only one of the native calendars and an import from file can only be done in a new calendar of type Uploaded file?
In that case, should I replace the two native calendars I want to combine with the new Uploaded file calendar and a new empty native calendar (default)?
Will new events created by members go inte the Uploaded files calendar?
Will all modules and menus stay intact (they refer to categories)?
Is there no simpler way? :-|
/Sven