To update your Boost My Mail application MSI deployment GPO; nothing could be easier!

1. go to the existing GPO 
2. Right click and click on "add a new package"
3. Go to the latest version of the MSI
4. Click on OK 

Check

You can verify that the new package is an upgrade from the previous version
And conversely, you can verify that the latest version of the package upgrades the previous version