I personally prefer to use "Kegety's unpbo tool
" (part of the armas tools, just check the readme for instructions).
As fence says you will need to unpbo the campaign pbo, search for the correct mission and copy that mission file to your
C:\Documents and Settings\your computer username\My documents\ArmA Other Profiles\your arma profile\missions
Than start the editor, load up the correct island (for this campaign it is Sahrani) and than choose the mission from the list. Now you can edit the mission.
The fact the creator didnt add any save possibilieties to the mission can have many reasons. maybe he tried it but never gotten it to work.
Adding the possibility to save a mission requires some good knowledge about SP scripting.
You may want to contact the creator first asking him if its possible to add. It would be a waste of your time to spent hours on while he tried it already without luck.
Since you can now edit the mission you can remove the number of enemy units at the area where you die all the time.
Also keep note you can lower the AI skill in your arma options menu ;)
btw, I have removed your question you submitted to our FAQ since you already figured out you should ask those questions in the forums :thumb