Bottom post of the previous page:
The injury report absolutely doesn't exist solely for gambling. I get what you're trying to say, though. I'm just saying that from the way I've read the rules on injury reporting it doesn't appear that the 49ers broke any NFL related rules whether it was objectively the wrong thing to do or not.
Edit: To my point, a guy who isn't even on the injury list could pull their hamstring during warm-ups and miss the game. Also, Mason said he was told on Friday that he'd be starting. We all know NFL lingo enough to know that doesn't mean he was told CMC wasn't going to play at all. Literally all that means it that he'd be taking the first snap (and presumably getting a fair amount of playing time).
Could be that they planned to use CMC in a limited fashion before re-evaluating and changing their mind yesterday.