I’m not actually sure what the mechanism behind the patches is. Whether they are microneedle or if they use an oily adhesive that modifies skin permiability.

I will note it is extremely slow, like it takes hours to reach steady state slow.

Again, if you are capable of aerasolising a substance such that you can reliably coat someone in it, and you are willing to break chemical weapons treaties, and you love warcrimes you can just use something more effective.

It is absolutely trivial to block the action of an opiate, they’re just not effective indiscriminate murder drugs.