Except the lesson is you can’t. Texas v. White resolved the legal issues, holding that the 1861-1865 pretended secession was of no legal effect, and that putting down the insurrection was correct. Further, it held that money loaned to support the insurrection should not be paid back by the States.
So you are pretty much wrong on all counts. Rather like saying you can rob a bank and shoot a guard with no penalty, and lets just pretend that getting caught, put on trial and executed part doesn’t count.
You have a rather simplistic view of things. Both sides were hypocrites. At the beginning, the South said "We Secede." The North said "You can't secede." When the war was over, the South said, "Okay, since we can't secede, we will send our Representatives and Senators back to Congress. The North said "No. You Seceded. "
Did they secede, or didn't they? I guess when the US wanted to regard them as having seceded, they did, and when it wanted to regard them as not having seceded, they did that as well.