I'm not sure that could always be assumed. Recent research in the Georgia vote indicates that secession did not even get a majority much less the strong super majority that would show the necessary popular support to warrant such a momentous regime change. There were also several reports of convention delegates pledged against secession voting for secession once the convention convened. Had Georgia rejected secession, the rebellion wouldn't have been sustainable even in the short term.
Tennessee's secession was just plain illegal, an action of the pro-slavery political class in the legislature against the expressed will of the people.
I only know of these two fraudulent secessions. Then again, these two states are the only cases I've studied.
I truly enjoy studying the history of the cause of the Civil War. My claim to fame on the subject is while I was in college, I rented an apartment in the home of the grand daughter of Governor Thomas Moore. His official portrait hung over her fireplace. I spent a lot of time sitting with her listening to her stories, which were quite fascinating. I wish I knew then what I know now as I would have taped her and captured all of her memories. I never knew her exact age but she was probably somewhere in her 90’s when she died. The home was beautiful, on Audubon Park in New Orleans, I hated leaving there but after she died her kids (who never came to see her) sold everything. They were in their 60’s and you could tell they were thrilled she was gone because they were finally able to inherit her money, which was quite a bit I might add.
The pertinent aspect to what happened back then is wether the Constitution was adhered to or not. I believe it was not and you believe it was. If the Federal government had prosecuted Jefferson Davis on the crimes he was charged with the issue would have been answered but he was not prosecuted. There are a number of sources who were intimately involved with the case back then that claim the government chose not to try him as there was a very strong possibility that they would lose the case. Just for academic sake, imagine that Davis was found not guilty of treason because it was not unconstitutional to secede.
I don’t think I have ever heard anyone refer to what occurred as regime change, no State tried to change the regime of the United States.
Prior to the firing on Ft. Sumter, the majority of Tennessee was against secession, afterward, it past by 108,339 votes for secession to 47,233 against secession. Eastern Tennessee was against it, the rest of the state was for it. Georgia voted for secession, there are claims there were voting irregularities in some counties. Keep in mind that the Constitution of the US was barely approved in many of the states, with only 5 having a super majority.
I am not for or against the north or the south in this conflict. I do however believe that these events started us down the path that we find ourselves on today where the Constitution is regularly disregarded and its’ meanings so twisted and perverted that no Founder, if brought back to life today would believe he was in the United States.