Hey Terry!
I haven’t seen the Haute Route program but can share the following thoughts pertaining to your question:
-For the strength you want to work on, if the Haute Route plan doesn’t already have gym specific workouts then I would add in those exercises to the gym workouts in the program
-For technique, since going downhill will work out the muscles you’re training, I would eliminate the most “ski specific” exercises but still do the remaining exercises in the workout plan for that day

For example:
Saturday gym workout contains plyometric squats + core. If you’re going skiing on Saturday, still do the workout but remove the squats and just do core (and whatever’s left).
I would think of it like “substituting” skiing for the leg specific workouts

Granted, if you have a huge ski day and your recovery/energy to do the remaining gym workout is dead, then adjust accordingly.

I think it also depends on what your resort days look like. If it’s a “normal” ski day, like Terry Lui said, you should probably do some strength work.

Also, because of time on lifts, the actual activity time is very low. I’ve timed it in a couple of different scenarios, from family ski days to hard-charging with friends. Ten minutes of activity per hour is pretty standard with kids in tow (if the kids can ski well). With aggressive friends, it’s usually somewhere between 12-15 minutes per hour.

So the same effect of a half-hour of a strength workout would probably take 2.5-3 hours of resort skiing.

Depending on the volume, a day of downhill skiing might be more like a muscular endurance workout than a strength workout.

Some other thoughts:
– Effects of the day will depend how much hiking you do inbounds. Steep hill at altitude carrying some gear should feel like weighted box steps. 🙂
– Terrain would also have a significant effect, e.g. moguls are going to impose more stress than corduroy.