the boj and bop files are just renamed .jpg and .png files. The reason why we did this is that players do not already view through all graphics before they even played the game. For modders, it is easy to go around that.
Irfanview for example shows that when trying to open these files with it and offers to rename them. In order to modify them you can use either Irfanview and its batch-converter/renamer or use a self-created batch file with notepad. The txt file contains just this line:
save it as a .bat file and run it. Same procedure for returning them to boj files for use in-game.