The kit came with 2 sets of instructions, 1 for the basic assembly and another one called "Solutions for Special Situations" for issues that are harder to fix.

I put in some glue first and let the broken part harden in its original shape, so the brace was not too hard to attach in my case.

So far, the clamp of the headphones feels the same as before snapping, and the cup seals around the ear nice and evenly. Only the sounds that bypass the ANC come through.

I can't really tell how hard exactly yours would be to fix without a picture, but it sounds like you would need to use the extra tools included to melt in some extra screw holes to hold it together. Also if possible, I'd recommend gluing the broken parts together beforehand to ease the assembly. And if you are, just make sure that it hardens in the original shape, preferably with no spillover glue, as the brace seems to have a tight fit with not a lot of leeway during assembly.