It's called planning.

Essentially you DO NOT want to change the key. Once you determine the key you want to leave it. Most singers can sing a few steps up or down. I had one who asked me to move the song one half a step. Seriously?

Anytime you move the key you end up with artifacts if you try to use a pitch changer of some sort to do it. Melodyne is the best for this process BUT.... it too will display artifacts for larger moves.

With BB & RB, moving a song to a different key is no big issue. It simply takes a bit of time and effort to render the tracks again in the new key and mix them. If you are using a DAW, it becomes a bit more complicated but not a brick wall to overcome.

There was a free mp3 pitch and tempo changer that did a reasonable job but it only worked with mp3's. You can google it.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.