Generally if the car meets Air quality control measures, and crash standards, then "usually" it is not too hard, although it will be expensive.
Being a BMW, it will meet crash standards in CH, but CH will have more stringent air quality standards than PA. If it was a California car, then it wouldn't be a problem...as CA actually has the strictest standards in the world (more than CH, D-Land and Sweden).
Unless the car has some enormous sentimental value, it will be much less stress just to buy a car in CH. Also, everything in your car will be American settings, and if you buy a car over there, you will have Metric everything. Also, servicing will be easier if you buy a CH car, as parts do vary from country to country.