double sided - single sided (export problem)

A couple of months ago, I made a Fa Mas (for those who don’t know, that’s a weapon) in Blender, but I wanted to export it as DXF and import it that way in Milkshape3D. It didn’t work, but I didn’t know why…
Now last week, when I was trying some things I never used before (like Subsurf), and checked out a bit more buttons (untill now, I only made sure I knew the things I needed), I saw the “Double Sided” button. Milkshape3D doesn’t use those, so I thought that might be the problem with the export/import thingy.
Now what I would like to know is: is it possible to just select the objects, deselect the “double sided” button, and then export it, or do I have to do this in Edit mode, or isn’t there an option to do that at all??
help me plz!
thanks in advantage,
Bentagon