How does a military measure change the Constitution? It can't. If the Southern states were still in the Union, as Lincoln claimed, he had no Constitutional authority to abolish slavery in any state. A State could abolish it, but not Lincoln. It takes an Amendment to change the Constitution.
“How does a military measure change the Constitution?”
Oh, boy. You’re not that obtuse, are you? Are you not aware that the president is the commander in chief of U.S. armed forces, and that the relationship between the citizens and the military is not the same in times of peace as when said citizens make war with the government?
Technically, the Emancipation didn't legally end slavery in the rebelling states. Read it. It never says that it's making slavery illegal in those states. It says that it's freeing the slaves. It's similar to a civil forfeiture in a drug case. When the government seizes a drug kingpin's house, car, boat and cash, they're not making the ownership of houses, cars, boats and cash illegal. Putting a legal end to slavery was accomplished via the 13th amendment and the Reconstruction state constitutions.