I have shapefiles containing polygons and lines that are used in a mapfile for projecting them through Mapserver. Is there a way in changing the projection of the layers by 180 degrees(i.e. upside down)?
If you want to rotate all of your layers, this can easily be accomplished by using the ANGLE attribute of the MAP object.
MAP ANGLE 180
Take a look at this wiki page for more info: http://trac.osgeo.org/mapserver/wiki/MapRotation
There are also some good caveats in the mapfile documentation: http://mapserver.org/mapfile/map.html#ANGLE
For instance, if you specify a layer angle, it will be calculated relative to the map angle.
Theoretically, I think this will work. If the map projection you're using has a scale factor, make it negative. If the false easting and false northing values are non-zero, make them negative too.
I haven't used MapServer so I don't know if it's possible or the details on how to do it.