“I think there is justification for many states to adjust their borders. Can it be done? Aside from miniscule border adjustments, has there ever been large-scale adjustments?”
Yes. Maine was carved out of Massachusetts. Vermont was denied to New York which claimed it. West Virginia was carved out of Virginia. The Michigan Upper Peninsula was taken from Wisconsin. etc.
Oregon and Washington were themselves taken from Britain/Canada.
But what about AFTER they became states?