When you click on decline, a file named usbtocloudinstalldeclined.txt is created. This prevents the installation request from coming back. If this file is deleted or the drive is formatted, this request will reappear when you log into the drive again.
To prevent accidental deletion of this file, right click on the file and choose properties. In the general tab under attributes, check the box next to Hidden and click OK. As long as your computer is not set up to see hidden files, it will not be seen. But be aware that formatting or resetting the drive will still delete the file.