COORDINATE SYSTEM FOR DGNDB CONCEPT STATION FILES

Hi

i have beeen trying to set the coordinate system for a new file using a custom coordinate system. I have read previous posts on a similar matter but there's no clear explanation on how to create a custom coordinate sysytem. 

But so far, i have been unsuccessful. Am trying to set my coordinate system to Arc 1960 36N.  I want to create a file and use it as my seed for the different projects. I tried using the geo-coordinates but it was showing an error and the map was not displaying.

And how do i remove the extents of a file with a set coordinate system?

Thanks