I know that SQL Injection is a good way to hack into a server and change what you want, steal what you want, or even crash the database, but I remember reading a thread on Mozilla forums where the posters agreed in conclusion that there are other methods, besides SQL injection, that you can change certain values hidden from the average users. Considering, they said, that certain values such as post count, join date, etc are simply accepted number values in a system, with the right methods the user could change such values to their liking.
Now, this is not about my account here, because I'm fine with everything, but I'm just wondering, are they right that there is a way besides SQL injection? Because that would mean that hacking in some cases is not required for someone to change certain hidden values they want changed. And would it even be legal to do so anyways? Editing the source code only changes things on your end for a short time.