And how can the Makefile be edited?
You can use any good text editor to edit a Makefile.
Code::Blocks should be able to edit a makefile; I have never used CB to edit a makefile, myself.
FYI: What to edit in a makefile is likely off topic for this website.
I suggest using standard CB project inside CB.
If you wish to use CMake generated CB custom makefiles you are NOT going to get much help on this site figuring out how to edit the makefile.
Note, to run the exe once you get it made; you might wish to try using the CB Tools or Toolplus Plugin.
If there a reason you are NOT using a standard CB project?
Tim S.