the skier wants to maintain knee extension into the turn finish.
Is is possible to maintain knee extension tension while simultaneously sitting or squatting?
It's hard to verbally describe, but this exercise may be helpful.
Stand on toes and squat slightly.
You butt is lowering and your knees are closing, but you're maintaining knee extension tension or you would collapse onto the floor.
Concentric tension. Extension tension is greater and positive.
I think in the above you are mixing some terms / confusing some terms.
Typically when we talk of joints (ankle, knee, hip) we talk of open and closing - but not "tension" which would be the muscles between the joints.
Or, at the whole body level we talk of extension and flexion
At the bottom of the turn most of the joints are closed, delaying the finish and allowing the skier to "swallow" some of the terrain
instead of being launched into the air. A ton of flexion here, (far more than in non-mogul skiing)
As soon as the bindings cross ridge/spine/crest, we extend again:
maintain ski:snow contact
give us back our full range of Flexion when we head for the next bump and do it all over again.
In mogul ski the rhythm is more "down-up"
down (ie flexion) as we hit the first mogul/spine/shoulder
up we extend on the back side and change direction