Its not as easy as simply unpacking and then modifing campaign. You can unpack and change whats in the squad and then repack. Heres a little write up I did for APOS (Works for SABOW too)
http://graviteam.com/forum/index.php?topic=10009.0. But this doesent even open up the editor. While i think its possible to unpack and thru a hell of alot of cut and paste get it to open in the editor, the time and effort is not worth it. Its easier in this case to unpack campaign, grab its DIV_POOL script and compile a new campaign the way you want it. Also be very wary of 4 movement nodes on all squares. You might set the AI one way but they do what they want. You only give general orders and then they decide whats best. I love it. I made Operation safari for SABOW and I really have only a hint of whats going to happen.
If you need help with any of this just ask.