how does one use these replacement keys?

Looks like it's just a casing and key blank. No electronics included so nothing to program.

If the objective is to get a key that will actually start the car. This probably isn't it if your original keys have a chip in them. These are for replacing a broken key by transferring the guts into the new housing & having the blank cut to match.

Thus spake "E. Meyer" :

And if the objective is to replace both the mechanical and electronic key, I haven't found a dealer in the approximate 50 mile radius of our house that will replace it without having proof of ownership and, sometimes, actually having the car at the dealership.

I've seen articles about the availability of the whole key from some "third parties".

Dillon Pyron wrote in news: snipped-for-privacy@4ax.com:

Same here. Some of the dealerships around here (and not just Honda) even have printouts stuck to wall advising this.

Typically they want not only you, personally, and the car's ownership papers, but your own personal photo ID as well. If you're a husband trying to get a key made for a car registered to your wife, they won't do that without her presenting her documentation in person.

The same people who hack into garage-door-opener signals so as to break into your house, I'll bet.

Shrug. Must be a regional thing. Local Chrysler dealer gave me the magic number, and pointed me at the outside locksmith they use. Most brands, if you have 2 working keys (the non-button kind, at least), you can get a key at any real locksmith, without the magic number. Not sure if Honda is like that, or they have to be different like they are with everything else. I've managed to not lose they keys that came with my 99 Honda, so never needed another one. My 05 dodge van came with 1 key, and it was one of those damn huge keys with the buttons, so I went to locksmith on the way home.

I had a friend who lost his last key. He had to get a tow to the dealer, because neither a AAA locksmith or dealer would come to the vehicle. fortunately the key service price was not too expensive.