You need to download Python 3 and then install Pygame (write `python -m pip install pygame` in your command prompt).
You should now be able to run the DUGA source code without needing an .exe file. To test if everything is correctly installed try opening the command prompt and write `python` and you should see something like `Type "help" , "copyright", "credits"....` etc. followed by `>>>`. Now write `import pygame` and if you see a greeting from pygame, it works.
Now you can run MAIN.py (perhaps right click and open with IDLE, a Python editor). You will now be able to edit the DUGA source code, and are not just limited to textures and sounds :-)
Let me know if it works out for you, otherwise I can give you some pointers.
Also, if you have a GitHub account, you can make your own fork of my source code. This way I can follow and see your edits :-)