NagaBaba

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.