Question [Q] Google Play Games High Score Hack

So, let's say HYPOTHETICALLY I wanted to change my high score of any given game in the Google Play Games app. I know how to change the xml file of the app to display a high score in the app but it doesn't upload that score to the Google Play Games server. I've seen people with outrageous high score (in the billions) and I want to know how they do it? Hypothetically speaking of course