My opinion is following:
I think that visiting a dojo by high ranking instructors from outside is a very tricky situation.Not only from etiquette point of view, but i.e. it can be seen as an attempt to take over a teaching.
That is why, such visit must be carefully prepared. Dojo-cho must be informed and agree to such visit. I personally witnessed situation, when a shihan that was invited to teach seminar(it was planned many months before), didn't even enter to the dojo unless dojo-cho personally went out to invite him.
If high ranking instructor doesn't care to inform dojo-cho in advance,but want to practice anyway, he should adopt very low profile(not mention at all his rank and experience), and simply practice as any other student, not expecting any special treatment. This way, he will avoid any awkward situation and will not put in bad position instructor that is teaching a class.This way he can show his respect for teaching instructor and for whole dojo.
This is about creating harmonious relations with unknown aikidokas and it is a common sense.
I agree. An instructor traveling on his own would be very careful about his welcome BEFORE coming in to the dojo. Many times senior people visiting other places will not mention their rank or experience so as to avoid the whole male "testing" thing that goes on sometimes. The thing is, if you've been around, you always know. A person who has trained to a high level in anything simply moves differently from one who hasn't. You don't want people to think you are being "sneaky" either.
This kind of thing can be very embarrassing... One of my friends is a very high ranking Hapkido teacher. He and his wife went to my old dojo and attended the Aikido class. The seniors were arrogant and treated him poorly. They didn't know who he was... he could have destroyed these fellows at the drop of a hat but he simply smiled a lot and then told me about it later. I was mortified. But then again, EVERYONE should be treated respectfully even when they aren't some big deal.
It's always best to call ahead. Better still to have an introduction. I'll get e-mails from teachers whose students are coming to town and wish to visit. That is the proper way to do things!