There is one website that says to use the hex editor in order to get 55,000 prestige points. What is the hex editor and how I use it to open my saved game and file 00002D80?

Also, does anyone out there know any useful cheat codes for PG2?

You can try this one:
https://mh-nexus.de/en/hxd/

But, I would recommend you seek help from anyone who is a programmer or knows how to use a hex editor. You can do serious damage to files and you can stop the operating system working if you do not know what you are doing.