I’ve never experienced this to be the case. I’ve purchased Macs in the various countries I’ve lived in, and when I moved from one country to the next it was never an issue to get service when needed. I always get AppleCare+ for my Macs so I’m not sure if that’s why, but there has never been a problem.
Also don’t get keyboard stickers - just replace the keys. You can get them from the Apple repair website or cheaper on Amazon or Ali Express. It’s really easy to change the keys. If you get them from Apple, there are no concerns about warranty being affected.