When working on a 2D project, there are two files which must be modified to change the default 3D settings for new drawings.
The .PCF File
The first is the project configuration file or the .PCF file which is named for the Town and Proj #. This file is project specific and is located in the "projects" directory under the MicroStation workspace. The variable in the PCF file that controls the seed file used for new drawings MS_DESIGNSEED. This is the file used when you issue the File -> New command. The PCF file typically does not contain the MS_DESIGNSEED variable and must be added for 2D projects. Add a new line containing the following text:
MS_DESIGNSEED = NHSEEDF2.DGN
MS_DESIGNSEED = NHSEEDM2.DGN
While you have this file open, check to see if there are other variables that need to be updated.
The .MSS File
The second file which controls DGN's created from MX drawings is the .MSS file. This file is named for the Town and Project # i.e. Holderness-11849.mss and resides in your project's PRJ directory. There are two variables in this file which determine weather the DGN created is 2D or 3D and they should be the same. Modify them to read:
To convert existing 3D files to 2D, use the File -> Export -> 2D command. The 2D DGN name can not be the same as the 3D DGN name. Typically the DGN is created and the batch files run in the PRJ directory and when I do the export I save the 2D DGN to the proper directory ie. the \CUT SHEET\CROSS SECTION or \CUT SHEET\PROFILE directory. The 3D version of the DGN in the PRJ directory can then be deleted.