The reason why most of static emplacements can be used only by the defending team in SP/Coop is to prevent the attacking team from losing its bots manning those MGs and AT guns as the offensive progresses forward. The emplacements (with the exception of the mortars) are coded so that bots, once entering them, can leave only by being killed, which makes sense for the "static defenses" kind of maps. As a result, on maps like Alam Halfa, while playing for the German team, you may end with a quarter of your teammates manning the MGs and AT guns only useful against your own main base.
If you still want to unlock emplacements, go to the respective GamePlayObjects.con, remove "ObjectTemplate.teamOnVehicle 1" from the respective object spawners and remove the following code at the start of the file for the respective emplacements:
ObjectTemplate.activeSafe PlayerControlObject <Emplacement name>
ObjectTemplate.dontClearTeamOnExit 1
Note, don't mix locked and unlocked object spawners for a single MG or AT gun on one map, this might end in CTDs.