How will my usage of manage.py and django-admin.py change with virtualenv?
No, only thing what virtualenv does, is that it creates an environment that has its own installation directories, that doesn’t share libraries with other virtualenv environments (and optionally doesn’t access the globally installed libraries either). Therefore it just means, that your project will use libraries and packages from virtualenv. So you won't have to change your manage.py.
I have completely shifted my all packages to virtualenv, but my project files were generated by the global Django installation.
I want to know what changes I need to make to the manage.py file, and do I need to use the virtualenv django-admin.py file now?