You can adjust what it targets as stoich but there is only one true stoich. The o2 sensors will adjust fuel trims to achieve stoich regardless of what you set it it. Hell you could set it at 9.8:1 but your only lying to it. And it would have to pull fuel out via trims. The set stoich is the base number for for all your fuel calculations. Again, with a closed loop system the computer is always going to want to achieve stoich. Unless you set PE to come in at idle and fudge your lambda table to run lean. Without checking I'm not sure if you can even command a lambda greater than 1 though