Hi Ulrich Kröpke

You are not far away with what you have done so far.
Goto data\Campaigns\CampaignProjects
open with text editor Happy_Times.py
At the bottom add:-
[Layer22] *****this should be the next number****
LayerType=0
MissionName=Light_Ships
Then goto the top line and change to add the extra layer:-
[Project]
NumLayers=23
Save are then restart "Happy times"