Change the local links to production links while grunt build?

Can we change the links in grunt which mostly will be local to production links during grunt build?

For e.g.

.a-container {
    background: url(../images/hello.jpg) no-repeat top center;
    background-size: 100%;
}

After build it should look like

.a-container {
    background: url(http://hello.com/blah/blah/hello.jpg) no-repeat top center;
    background-size: 100%;
}

We have the URL upfront which can be configured in grunt file.

If you're not stuck using raw CSS, I'd recommend throwing grunt-contrib-compass on top of the project. You'll be able to set dev/production environments and run them when you want. You'll specifically want to look at the option for images. I structure mine in the following way:

compass: {
  dev: {
    sassDir: 'build/sass',
    cssDir: 'stylesheets',
    imagesDir: 'build/assets/images/'
  },
  production: {
    sassDir: 'build/sass',
    cssDir: 'stylesheets',
    imagesDir: 'http://example.com/images'
  },
}

You don't have to necessarily leverage other parts of sass/comapss (though there will be some upfront work switching the directory and file structure around).

If this approach doesn't work for you, you may want to take a look at Yeomans usemin task. Unfortunately, I'm not as familiar with that one and can't provide much help with it.

To complete the question which I started off, here how you can achieve it.

        compass: {
              dist: {
               options: {
                 config: 'app/config.rb',
                 sassDir: 'app/styles',
                 cssDir: 'dist/styles',
                 imagesDir: 'app/images/',
                 javascriptsDir: 'app/scripts',
                 fontsDir: 'app/styles/fonts',
                 importPath: 'app/components',
                 outputStyle: 'compressed',
            },
        },
     }

And you should have a config.rb file as Compass doesn't expose some options as command line arguments. 

config.rb

http_images_path = "http://cdn.example.com/images/"

Also in your sass/scss files don't forget to use, image_url('hello.jpg') instead of only url('hello.jpg') , url() is ignored by Compass.

Next time when you run grunt compass:dist you will have the urls baked into the generated css files.