I love the focus on retraction edge changes!
That being said, I hardly ever approach that first with complete bump newbies. For an awful lot of skiers, that is too big of a fundamental change to their skiing to tackle within a newbie bump lesson and will generally cause confusion and mental overload.
Some bare bones requisites before trying bumps, I want to see really good upper/lower separation, and fairly disciplined upper body. Decent balance. Able to do side slips and forward side slips. Able to do some basic pivot slips or something close to it that represents a short radius turn which is pivoty or short-swingy with the upper body maintaining discipline of facing down the fall line. If they can't do that, then no matter what you do in the bumps they will be fighting against their own progress. If I am satisfied they can do those things on the groomer, and they are bump newbies, then we go to some easy bumps and I will talk about tactics and line choice and help them use the skills they already possess to ski through the bumps.
If students don't meet the above requisites I mentioned above, then I don't like to take them to bumps. I would rather work on those skills first until I'm satisfied that they truly are ready for the bumps. Take a skier into a bump run without those skills and they will go into survival mode, probably ingraining worse things. Some clients are insistent they want to try some bumps anyway. Ok, then find some really easy ones where it can be done safely and after they flail around a bit in those easy bumps, point out issues related to the above prerequisites and take them back to a groomer to work on those things.
Presuming that they meet my criteria......
I like to start newbies with a forward side slipping approach. Some people have talked about side slipping down the face of the bump, but I get a little more specific then that. I want them to side slip down the side or shoulder of each bump with the skis perpendicular to the micro fall line of that side bump face (diagonal to the overall slope fall line), and when past the bump, pivot the skis to face the other direction and side slip down that next bump side/shoulder, etc.
This is very important because this is the line I want them to learn to take. Eventually their side slips can turn into forward side slips on that side face (which is pretty much the same as making a turn down the fall line, using the edges on the side of the bump there. As they get better at this they will find themselves automatically taking the right line and getting edge purchase in the right places making their own turns through a bump field.
An easier alternative is to use this approach but skip back and forth between two adjacent zipper lines, so that they have more time in between each side slip. So side slip down the side of one, as they reach the bottom of that little face, forward slip around the bottom of that bump, skip over to the next line over and make a pivoty turn and do the same thing there. Help them visualize where are these side faces I want them to engage their edges and side slip. I call it the "sweet spot" and help them to identify the sweet spot. We spend a lot of time talking about the sweet spot, how to see it and use the edges to side slip on it and when to make a turn to get the edges on the next sweet spot, etc. This usually naturally will evolve into them making the turns they already own throughout a bump field and learning to choose the right line to do so.
General relaxation and absorption is also a good idea to cover, show them how to flex and extend their legs like shock absorbers and to think in 3D that way, which is possibly something they haven't put a lot of thought into before now. Straight run them through bumps, become aware of the the shock absorbers they possess.
I don't like to get so technical with the whole retraction release idea, which in my view *IS* an important aspect of good bump skiing, but too much for first time bump students. Its confusing and difficult for them. However, if you have time you can sometimes get a little yardage out of getting them to learn that movement without trying to explain it to them. Find a ridge and make turns across the ridge where they are told to change edges right on the top of the ridge and to keep the skis on the snow. You'll see retraction turns appear out of nowhere. If you can't find a ridge, use the edge of a cat track or trail if you know of a safe one to use. Go back and forth on and off the cat track, same thing, keep skis on the snow. But I do not view that as first time bump lesson material, in my mind that comes later. Getting into a deep technical discussion bout how to flex on the top of a bump and time a pole plant with a retraction edge change, extending into the trough, etc...whew that is a lot for a first timer. IMHO too much.
Blocking pole plants, also I feel is more advanced topic, but if there is time to work that in near the end to remind them to make a pole plant while they look for the sweet spots to side slip on, ok.
IMHO, take the skills they already own and show them how to navigate safely, with a big smile through some blue bumps. Focus on line choice, simple tactics like looking ahead and using their edges in the right places that make sense that will naturally evolve into turns through bumps.
Students that are already high level skiers that want to learn to ski black bumps and beyond, that's where it makes more sense to get into some of the technical points that have been brought up so far.