When you learn an IR command, HA saves it to a config file which is specific to that IR blaster. If you want to be able to send that command from another blaster, you’ll need to work out which config file matches the two blaster, then manually copy across the codes.
I can’t be the only person who wants to be able to control devices which move around the house, or who has multiples of the same device.
Ideally IR codes would be stored centrally in one place, to be accessed by all IR blasters, but failing that having a way to automatically, or upon request, sync codes from 1 blaster to others would be great too.