You do not need a code to register a horse on howrse. You make an account.
There are currently no available promotional codes for Howrse.
no
The url for the international howrse is linked below and you can reach the others from the site.
no
yes. it is.
there are none
Ask nicely
there isn't one
there are none
I believe that you can enter it on the Card code page.
Because they have been used or howrse won't allow that code anymore.