Historically, I was very concerned with this issue. Then, in 2017, I was selected to work the North/South all star game in July. I was going to work back judge. I had never worked 7 man mechanics before, let alone as a back judge. And I hadn't worked as a 5 man back judge in many years. But I was pleasantly surprised at how easy it was to pick up the 7 man mechanics. There are some different coverages and keys, but there are also significant reductions in responsibilities simply because you have two extra officials. From that experience, I concluded that the advantages of working 7 officials greatly outweigh the potential complications of asking people to pick up some mechanics with which they are unfamiliar in the week before the game. Plainly speaking, it's just not that difficult.