In the new Minecraft 1.17 update the ores are changed; I don't like it at all. Can I somehow prevent the ores from being changed?
Yes, with a texturepack.
Don't play on the version
You could possibly use a different texture pack, or play on a different version.
Just don't play on the new version, then you won't have the changes either
If you are only bothered by the textures of the ores you can create your own texture pack.
You then swap the .png graphics with the old graphics accordingly, pack it up and then load it into your mc. Of course, you can't remove ores that are completely new, they remain in the game