You may freely modify MyKaryotes as long as your changes are made to the provided source file and are recompiled to create a new executable. That version of the modified source you create is the version which must be redistributed with the executable you create. YOU MAY NOT DECOMPILE THE PROVIDED EXECUTABLE UNDER ANY CIRCUMSTANCES; this is frowned upon in the Game Maker community, and part of the reason the source is provided is to make this unnecessary.
Any derivatives you create must also be distributed under this same license, albeit with copyright information changed for your version. You should keep this license freely accessible in the F1 Game Information text and in a separate LICENSE.txt file.