Okay, I found one solution where you need to know, which objects are existing. The GetObjectFromPath command was correct, but used in a wrong way.
You must create a handler to the object:
handler.Redu_Station = STK.root.GetObjectFromPath('/Facility/Redu_Station');
where it is important that the path points to the current working directory. Facility here is not a folder, it is the type of the object you want to access.
If you want to access a satellite, you need to write something like
handler.MySat = STK.root.GetObjectFromPath('/Satellite/MySat');
After creating that handler you can access the object by simply using
MySat.SPA.bound_radius = 3; % [m]
MySat.EPS.PanelGroupName = 'Panels'; % defined in the spacecraft model for STK
CmdString = ['VO */Satellite/MySat SolarPanel ' ...
'Visualization Radius On ', num2str(MySat.SPA.bound_radius),...
' AddGroup ',MySat.EPS.PanelGroupName]
STK.root.ExecuteCommand(CmdString);
I hope this helps.