If you mean this by the CE3 Free SDK then you do the following:
1. Place a grunt; RollupBar, Entity, AI, grunt.
2. Go to entity properties, Faction and then change it to the desired faction;
1 Civilians don't do anything (unless you script them with the flow graph)
2 Players are friendly, attacks enemies.
3 Grunts are enemies, attacks friendlies (you).
3. reload script; in the entity script section (below entity property).
Hope this helps.