When skiing into counter the pelvic shift is not something you actively do, it's something that just happens.  

When skiing into counter, your upper body and pelvis  simply maintain the countered position they had in the previous turn, as you go through the transition and into the new turn.  That means at the beginning of the new turn you're facing more downhill, while your skis are still point more across the hill.   As you go through the turn you simply maintain that pelvic and upper body directional orientation while your skis turn beneath you, until you've attained the desired amount of counter.  At that point the pelvis begins turning along with the skis.  

When you do a pelvic shift, you execute it during the transition.  You don't maintain the counter from the previous turn, as you do when skiing into counter.  Instead, you drive your new inside (downhill) hip forward as you roll off your edges and finish the old turn.  By the time you begin your new turn, your inside hip drive should have already created an initial state of counter.  That initial amount of counter will be minor.  Just enough to allow your new outside foot to pronate.   As you go through the turn, and increase your edge angle, you gradually increase the counter to the amount needed to allow you to maintain balance on your outside ski.  Bigger edge angles call for more angulation to stay outside ski balanced, and counter allows for more angulation.