What changes must I make to the .pro file if I want to execute chmod command, execute the output binary file, or do some other operations.
The right answer depends on exactly what you want, and when. However, as seen in some previously posted comments here QMAKE_POST_LINK is probably what you want rather than POST_TARGETDEPS.
Check out this related post: QMake: execute script after build
For one, when you use POST_TARGETDEPS that fires off BEFORE your exe is created (in Windows) or BEFORE it is recreated (in Linux)! QMake works differently depending upon the platform and the complier.
I needed to do some "symbols processing" on an exe when it was recompiled. POST_TARGETDEPS gave me problems in both Windows (using mingw) and Linux (using gcc). In Windows, it executed my script prematurely, and in Linux it overwrote my exe after I had modified it (i.e. added back my debugging info to the exe after I had stripped it in my external script). QMAKE_POST_LINK worked perfectly, however, in both cases. It's also short, sweet, and more clear by comparison!