Yes, it's possible to install Sardinia Photoreal in both FSX and P3D because that's the way it was created. However, the developers insists in installing all the parts, not only the 1st one. There is a page where you can see all the add-ons available for downloading.
Download page: http://www.rikoooo.com/en/downloads/viewdownload/68/704
The packages feature Windows installers to make it easier to deploy the content, but it requires to have FSX installed and ready to be started.