Yet another question - how can a transition between 2 world files (levels) can be done in crystal space?
Is it necesseray to reload the entire Crystal Space application with another filename as a parameter for the LoadMap() function or can references be setup inside the worldfile itself?
You cannot do this from within a world file but you can easily add code to handle this. Most games that need this feature use this with a portal to another sector where the destination sector is part of another map and thus not loaded yet. As soon as that sector is needed the engine can call a callback in your application (check out the iPortal api for how to do that) and then you can start loading that level.
If you use CEL then the zone manager in CEL automates this for you.