All published GPS approaches known to Jeppesen (Navigraph) or LIDO (Aerosoft) are flyable using our GPS.
However, the databases of Navigraph or Aerosoft simply flag the approaches as being GPS approaches, without a further distinction which kind of precision is required to fly them, and whether they require WAAS, LAAS or EGNOS support. Obviously, the GPS position accuracy in X-Plane is always 100%, so the approaches can always be flown to the lowest minimum. In real life however, GPS alone is never 100% accurate and reliable, so some approaches will require augmentation equipment, like WAAS in the US and EGNOS in Europe. Depending on the requirements, the GPS approaches are flagged with further distinctions on their accuracy, and can only be flown to that accuracy if the augmentation equipment is operational. This is a distinction we do not make in X-Plane, as we always assume the GPS to be 100% reliable.
As far as X-Plane is concerned, all GPS approaches look the same, whether they are LNAV accuracy (non-WAAS) or LPV accuracy (WAAS required).
As our GPSs database is derived from ARINC424.20, the final approach segment would need to be encoded in the format understood by our GPS (we are contractually obligated not to use raw data, because of the risk of unlawful use of that data for non-flight simulation applications).
That means, to test custom final approach segments with our GPS, the approach needs to be encoded in a text file, probably by simply editing the procedure text file for that airport as it is shipped with X-Plane.
Editing these procedure text files is possible. The data description is in the attached PDF. http://questions.x-plane.com/?qa=blob&qa_blobid=17717992854988388477