Language- The most innocuous of all. Of all the changes this is the most likely to happen naturally. If we survive for another thousand years a common language is likely. The common language I would wish for would be rich and creative.

Multi lingualism is helpful but limitations are obvious when we attempt translations and arrive at wrong conclusions. Stories of the Japanese surrender negotiations are an example of this.

Race- Pick one or be creative. A nice blue sounds good to me. Skin color and features have nothing to do with diversity. Chinese would still invent gunpowder and use chop sticks if they spoke a common language and looked the same as everyone else. In fact, I specified this by including the "no retro consequences clause".

Civil wars prove that we would find reasons to hate each other. The intent is not to solve everything but to help in the least intrusive way.

Religion- More people have been killed in the name of religion than any difference in language or skin color. In a world where most are compelled to project some kind of afterlife it would be presumptuous to eliminate religion. To change this would change the basic nature of humanity. The best compromise I could think of was to eliminate the prophets and moderate the level of belief. The option of atheism would still exist.