I am just rereading this helpful advice, and this lead me to another question. What if there is no room on the run to really finish the turn? This weekend I did a black run that had icy patches on one side and moguls on the other. In between them there was a narrow corridor with some snow, and that’s the path I chose to take. Making wider turns meant either ending up on ice or in moguls, so I was doing shorter turns to stay in the narrow corridor. How does the advice above work in this situation?
On such advanced/expert terrain as you describe, you need the advanced/expert skill of making very short radius turns within that narrow corridor. It's an expert skill to keep grip while making those super short turns. If the skier is even slightly aft, the skis won't grip. If the skier doesn't get the skis gripping before they point downhill, they will skid out. If the skier has too much weight on the inside ski, the skis will skid out.
Manually turning the skis to make a turn shorter than the skis want to make, a super short radius turn, and keeping them gripping as you do that, when the snow is not hero snow, is a skill that separates experts from advanced skiers.
To bypass the issue of skill development and stay in control on that narrow lane of ice, try stem-step turns. Pick up the new outside ski (at that point the uphill ski), set it down
on edge to make a wedge, then stand on it. Pick up the new inside ski to get it out of the way. That new outside ski should take you around to a stop if you balance on it properly. In other words, the pivot you have to make to get such short radius turns is in the air, so it doesn't dislodge the new outside ski's grip. Repeat for the other direction.
One can go straight downhill in a very narrow corridor doing this, coming to a complete stop with each turn doing stem-step turns. Don't get aft on that lifted and pivoted ski; set it down a bit back so your weight will be forward on it, pick up the new inside ski slightly to get it out of the way and to be sure your weight is on the other ski, and around you'll go to a stop. Practice stem-steps ahead of time on groomers to learn how to stay in a corridor as wide as a log; in other words, doing no left-right travel.
Stem-steps will be difficult if your skis are wide, and easier if your skis are narrow.
Another option: simply side-slip, and do falling-leaf to keep yourself in the lane. Side-slips and falling-leafs are intermediate skills. Novices need to start learning these since they can save one when over-terrained.
Another option: do pivot-slips all the way down. Pivot slips are an advanced skill that take time to learn. They will give you no extra control over side-slips, but they look better if there's a chair beside the trail. But then if one can do pivot-slips, the bumps may be the more fun option.
Speaking of which, if you can do the stem-steps in the narrow corridor, you can try them in the bumps next time. That's a way of getting down bumps that are too difficult for one's current bump skill level.
@snoWYmonkey may have good advice that is different from mine.