I wasn't aware there was a provision for colonies amending the British constitution. That could have saved us a great deal of trouble in 1776 and onward.
I'm sorry to say "might makes right" is a staple of human history. Nations will always employ it. The questions are how much might? and for what purposes? One has to be careful not to throw the baby out with the bath when cleaning up the house.
As you know, there was no British Constitution. The King was sovereign, and he did not agree. That is why we had to fight for our freedom. The colonists won in 1781, the Southerners lost in 1865.
We can twist the pretzel as many ways as we wish, but this was the only difference.
Peace.