Absolutely! Short term, a tank or two, it' won't hurt anything. My concern would be using cheap low octane over the life of the vehicle.I would feel like it's safe to say, if you are in a pinch and you cannot get 91+ you'd be safe to run 87 until you can get to 91+.
Is that an accurate assumption?
Long term, your assessment of this seems very logical and makes perfect sense to me.
Anything in a pinch. Just get back to the "good" stuff as soon as possible/resonalble.