Yes you can extract them fom the ca folder. All compositon are there. So you simpley can edit them.I has made a small example with the most opject compositions.
So you only need to copy and paste the Object Location from the Editor.
All compositions get call via the Location Name via the init.sqf file
All composition you find in this mission map in location "Composition_direct_Load.Chernarus\dyno\data\scripts\compositions" and get loated directly from there. So it`s easyer to edit of load custom Compositions.
Also i thing is mp compatible.!!!
You can download the Demo Mission there:
http://www.4shared.com/folder/c_8Tvg5J/_online.html