How can I add, smack source as module in existing android studio project, so that I can use the smack without gradle and can even change certain files, as per requirement, I tried to import the project as a module many times, but failed and it was not working as expected.
There is often no sensible reason for doing so when people ask for that. Smack is extensible in most places where it is required, hence you should never feel the need to hack the source besides for bugfixes (which should go upstream anyway).
What exactly are you trying to achieve?