It has occurred to me that the Agasha School is unable to learn the 'Blessing of Steel' ritual, because it requires the Artisan tag. Has anyone seen a way to gain access to the ritual by picking up the school tag, or some other way I haven't thought of?

Not at the moment. The updated FAQ says that unless a technique 'slot' calls out the ability by name, you can't ignore other restrictions like clan, so I guess not.

At the moment there's no way to pick up the school tag, but you can pick up clan 'tags' via a title (Twenty-Goblin Crab) so I guess something akin would work if you wanted to create an Agasha smith?