If you will have it modified the driveshaft shop will need the shaft section complete with a yoke on each end. That way if/when they cut one end off and weld it or another back on they can align that yoke correctly with the yoke on the other end.
So you could pull apart the slip yoke to remove the back end of the shaft, but you also need to remove the slip yoke from the vehicle.
To illustrate how the slip yoke is assembled look at page 6 in this PDF, the exact yoke you have may be on that page, and if not the picture is still good.
http://www.drive-lines.com/catalogs/pdf/dana/J300P-3.pdf
