While it is possible to re-contour porcelain restorations once they are cemented, there is a certain risk of damage to the porcelain occurring and even with great care this can potentially result. The use of high speed rotary diamond instruments can be used to recontour porcelain and these in conjunction with various slow speed polishers can bring a certain amount of the luster back, but it isn't truly the same as the glaze covering the surface which you will be removing (that glaze is the final addition when the porcelain restoration was fired in the oven at well over 1000 degrees Fahrenheit and so can't be replaced in the mouth). Areas of porcelain that do not have glaze, or which are not highly polished, will be more likely to pick up stain. One of the risks is that the porcelain restoration can potentially develop a crack or fracture, and in many cases that would ultimately lead to it needing replacement, and with that the challenges of remaking one restoration to match another (it is much easier when multiple teeth are fabricated simultaneously). Also, without being able to measure how thick the restoration is in the area you are adjusting (and this really is not possible once the restoration has been cemented unless you have access to the original working models that the restorations were made from), there would be a greater risk of perforating the restoration if a substantial change was being made (and so creating a hole in the porcelain in which tooth or cement shows through). From a practicality point of view, it is very difficult, and then at some point not possible, to get these polishing instruments in between the teeth as you approach the area where one tooth touches the neighboring adjacent tooth (we call this area the facial embrasure). So there are limits to what can be done unless someone willingly opens up space between the porcelain restoration and the adjacent tooth which, as you alluded to, would then require adding some sort of restorative material to the adjacent tooth if it is a natural tooth. Ultimately the decision to be made by you is whether the potential for improvement to the shape is worth taking on the risk of damaging the restoration. Perhaps it is if you really are not happy. I hope this information helps in your decision-making. Best of luck! Dr. Geen