How to add a Geographic Coordinate System in a whole project?

Hello! 

I have created a new workset for a project. All the project will be designed in the same geographic coordinate system. I will have to create differents dgn models (terrain, corridors, drainange, urban services, etc). Is it possible to configure the workset to determine the same coordinate system for all the dgn files? or have I to configure the coordinate system in every single file I create for the project?

Thank you very much