A while back I was modding a game project and was able to replace some of the games hardcoded images like the main menu logo and some in game UI that was within the games exe. I don't remember how I did it sadly but I do remember I used some 3rd party program that was able to open up the .exe (or .dll) and replace some of the files. All I remember is I was not able to insert a image larger in size than the one I was replacing because it would overwrite code and damage the file. Does this make any sense?

I do have Hexedit and resource hacker but it doesn't do the trick...
The game I modified was Super Mario Bros. X