Here’s how you can install Geo-Shift add-on manually without Chrome store.
1. Download the Geo-Shift for Chrome zip file.
2. Unzip the file.
3. Go to chrome://extensions/ and check the box for Developer mode in the top right.
4. Click the Load Unpacked button and select the unzipped folder for your extension to install it.
Rest of the setup instructions you can see in this tutorial (Point#2 onwards).