Oh Wow - me and my big mouth. I don't recall saying exactly "skiing with them into effective movements", but I can see where that is implied. You've come up with a good list to which I'd at least add mental and gear. Mental being at least attitude and awareness. Gear includes pros on gear that's holding back their progress and pros that need to experience different kinds of gear to expand their horizons. To directly answer your question about meaningful change, I don't know. Most people I work with tell me I've helped. Some, I'm sure, we're only being kind. Sometimes progress is immediate and obvious, sometimes not. We've certainly had successes that have been a team effort and only meaningful after years of effort. We've certainly had our failures. The one common thread behind meaningful change is the skiers desire for change. I've been successful with a few stealth efforts to get some folks to improve, but I've also met folks I couldn't change with any of my tricks.
Every case is different. When I take on a "project" I have to get to know the skier and I never know where that will lead. Maybe a few stories can help explain.
"Evil Rusty" came about when I noticed one of our junior instructors doing the "intermediate plateau" thing. She was doing relatively great open parallel skidded turns. They were a little sloppy but perfectly suitable for safely navigating our intermediate terrain. There was obviously no awareness of the possibility to work the skis more on this terrain to gain the skills to perform efficiently on more advanced terrain. I could see that in her mind, because she could ski the advanced terrain, there was no need to get any better. Juniors typically don't get a lot of clinic time and I could see that she was headed for dead end skiing. So I took her out for a let's go ski session at the end of one day instead of just packing up to go home. After a fun (i.e. warm up) run, I asked her if she wanted a tip. When she said yes, I had her follow me for a series of short turns. I waited until she got synced up in an easy rhythm before I subtly reduced the skidding in the turns to slowly speed up without changing the turn shape or the rhythm. As soon as I could see that she had sensed she was falling behind and started to cheat to try to catch up I switched to very carved short turns and "leapt" way ahead of her, then stopped to let her catch up. After the third iteration of this with no feedback, she skied up to me and proclaimed "you'rrrrrrrrre eeeeeevil" (hence - evil rusty). She knew about edging and carving but she had no awareness that she had plateaued or what the next level of performance was and had no need to improve. But seeing that performance happen right in front of her and not being able to turn it on to keep up opened her eyes and motivated her. There may not have been meaningful change that season, but it was a least a meaningful first step. The Evil Rusty concept is useful when there is a mental block that is the primary thing holding back progress. You have to identify the mental block then design an exercise that will induce so much frustration/overemphasize the performance flaw/demonstrate an "impossible" task being accomplished with ease that the mental block simply explodes with an "aha" realization. Working around a mental block to chip away at it is usually preferred, but in rare cases extreme measures are called for.
Riding up the chair over our bump run, I often saw a couple of our older pros navigating the bump run methodically. These guys were feeding off each other and there was nothing "wrong" with their bump skiing other than it hurt to watch them because I knew their approach was a dead end and they could ski the bumps so much better, Both of them had the same basic problem: they were wayyyy to slow and that caused them to do a lot more work than they needed to. Since I knew them both fairly well, I made it a personal goal to help them both if only to relieve my eyes. But I had to work with them separately. I was working with one of them one day (I offered "you want some help" and he said yes). We were working on turn mechanics when another trainer joined us, asked what we were working on, and politely offered us a better solution. My victim thanked him politely, said "he'd look into it, but wanted to continue what we were currently working on. After that guy left, my victim stopped and explained why he liked working with me better. The reason the better solution didn't work for him was because of a physical issue the guy was unable to fix. He hadn't told me about it before, but he could tell that I had guessed about the limitation and was giving him a workaround that was actually working for him. I had not consciously guessed about a physical limitation, but I could see the standard approach hadn't worked for him. I never did get this guy to go much faster in the bumps, but I did get him to shape his turns in the bumps a lot more and put a lot more pep into his groomed run skiing. That was meaningful enough change to make him a happier skier and meaningful enough for me to see his technical level bump up a bit. The other guy is a longer story.
On one of the rare powder days at my home mountain, I came across one of our better instructors struggling in it. I gave him the "make your turns in slow motion" tip, let him follow me for a run and voila - problem solved. Sometimes you can make friends on a powder day.
I can't tell you how many clinics I've taken out on rental gear. In the old days, the learning opportunity was just "Jeez - no wonder the students can't buy a turn". Lately, the super intense feedback the modern rentals have even doing beginner drills can be eye opening. But the opportunity to have fun runs and open these baby's up let's pros experience a playfulness that they can incorporate into their "regular" skiing. The feedback you can get from a 7M radius ski can induce a new intensity of movements on "regular" skis that would take a lot longer to happen otherwise. Personally, I learned a lot from a clinic where we did a few runs a 130m ski on one foot and our regular ski on the other.
The key thing I've found for being a trainer is to make yourself available. Be seen answering questions and others will be more willing to approach you with theirs. Take time to hang out at the end of the day instead of just taking off so more people can "run into you", Be willing to put your gear back on go out for an extra run. Follow up with your clinic "victims" to seek feedback on the things you've given them. Ask more questions when you teach. Let the questions do the teaching. When you take clinics, watch how the clinicians teach instead of just focusing on what they're teaching. Steal their best stuff. Lots of folks teach for the opportunity to get taught themselves. If you've done your homework, you ought to be able to help them with something. After all, if we can do it for our guests we can certainly do it for the staff. There aren't many mistakes I've seen out on the slopes that I haven't already done myself (over and over again).