Gmolfoot makes a good point--hope we haven't confused anyone on this! Mounting cants (thin wedge-shaped plastic plates) between the binding and the ski is the long-established semi-permanent method of compensating for over/underedged alignment. It does NOT interfere with the binding-boot interface, as Gmolfoot states.
It is the temporary, experimental use of small cant strips taped to the boot sole, or just stuffed between the boot and the binding, that raises the liability--and possibly real safety--concerns. In my opinion, though, this experimental step is necessary to determine the optimal canting solution, before mounting cant strips beneath the binding.
The most permanent canting solution, as Gmolfoot also notes, involves grinding the boot sole to an angle. This solution adjusts your BOOTS, not your skis, so you can use any ski, and you can also switch your skis left and right--which you cannot do with cants mounted beneath the bindings. This grinding should only be done by an expert, with the right precision equipment and materials. And it DOES affect the boot-binding interface, so again, liability COULD be a concern if not done properly.
The DIN standard specifies the shape and the materials of the boot sole. Binding mechanisms are designed around this specified shape. They may not work properly if it is modified. And friction is a major issue in binding function, so different materials could also cause problems.
After grinding the soles, the "lips" on the boot toe and heel must be restored to the DIN-standard thickness and shape (top and bottom surfaces parallel). This can be done by either adding material to the top--often some sort of epoxy (non-DIN)--and grinding it down to shape, or by adding a plate to the bottom of the boot sole to restore its thickness after grinding, and then grinding the top of the lip parallel to the bottom. This second method is the current state of the art, as it compromises the DIN-standard the least, and the plates on the bottom are replaceable as they wear. Those manufactured plates are made of DIN-standard material and shape, so no non-DIN material needs to be added to the lip.
Again, it should be obvious that serious boot modification--especially sole grinding--should only be done by a knowledgeable specialist like Gmolfoot, using precision tools and proper materials. It's hardly a home remedy for canting needs. It's pretty hard to ungrind a boot!
While this thread arose from legal liability concerns, we should be aware that there are real-world safety and performance issues at stake.
Gmolfoot--thanks for jumping in!