If you're talking about the key that goes into the ignition, then you'll most likely need Honda to program/cut it for you (which will cost an arm and a leg).
Theres a code stored in the key. If it is not recognised by the ECU the immobiliser would be activated.
I've heard of ppl saying that some key cutting places can do it etc etc but I've had no personal experience with them.

With the remote transponder, if you buy a genuine remote transponder then theyre easy to program.

Or are you talking about buying a different remote/key for your car? E.g. From an Accord Euro or something?