I can only provide you with anecdotes, but when we tried this in Oregon 10 years ago for my husband, we could not get them to waive the 12-month residency requirement. He wound up using the Western Undergraduate Exchange program (we moved from Idaho for me to attend grad school), which is about 1.5x the cost of in-state tuition instead of out-of-state, which is ~3x. Unfortunately, when he exceeded a certain number of credits on his transcript, he was again charged out-of-state tuition even though we'd been living there three years and would go on to live there another three (Oregon driver's licences, long-term lease, etc.). He had to drop to below the credit threshold for a year because he had too much of his degree left to have paying out-of-state make sense.
My mom recently tried this in North Carolina and they also wouldn't waive the 12-month residency requirement even though she moved there approximately 11 months and 2 weeks before the start of the term she was applying for. They literally asked her what day she crossed state lines into NC and that was the day they were going to put that she was eligible for in-state tuition. Technically since she didn't have resident status at the start of term, she was SOL.
It's one of those situations where I understand why the rule is there, but it can make life very frustrating.