A.J.,
I don't know your specific situation so please bear with me if I mention something you already know. As a general matter, you can register your Mondeo Vignale in Virginia. However, it will almost certainly cost you a bit of extra money, a lot of time, and a significant amount of aggravation.
First, keep in mind that you are dealing with unionized state workers in a department that is the butt of jokes in EVERY jurisdiction of the country for surly, lazy employees and YOU asked them to do something that isn't part of their normal day. YOU asked them to THINK -- How dare you! I'm sure your request was the topic of conversation. After addressing the items discussed below go back to the DMV and try the process again with another clerk. If you raised your voice or insulted the clerk you should go to a different DMV office.
Second, did you import the vehicle or did you buy it from someone else? If you bought it from someone else your chances of registering the car are pretty slim because you likely won't have the foreign paperwork you'll need. As for the paperwork, you'll need the foreign title and bill of sale. If the documents are in a foreign language you'll need a certified translation as well (you have to prove the car wasn't stolen). You'll also need all of the importation documents; waybill, customs release, EPA and NHSTA forms, and the like.
Third, are you SURE that all of the parts in the vehicle meet US standards? Even if your vehicle was built to meet both US and the foreign specs, the chances are that any aftermarket changes will NOT meet US specs and will need to be "fixed." Hell, even a replacement for a cracked windshield many not meet US specs and will need to be replaced before you register the car.
Fourth, take a look at the VIN. I bet it doesn't fit the standard US configuration. If not, the police will need to find each of the VIN locations on your vehicle, make sure they match, and run the VINs through INTERPOL to make sure the car isn't stolen. The DMV can't do it themselves. After the police are satisfied the care isn't stolen you'll need to convince the DMV to make new US-standardized VIN plates and have them installed on the vehicle.
Last, once everything else is in order, you'll need to be prepared to answer stupid questions from the DMV clerk. For example, your odometer is almost certainly in kilometers instead of miles. You'll also likely be faced with disbelief that your car is actually a Ford.
As a separate matter, you mentioned registering the vehicle in another state. If the car is going to be in Virginia DON'T do it. If you drive a car with out of state plates around NOVA it will only be a matter of time before someone turns you in as a tax evader. Fairfax will send the police to check if someone turns you in on
https://www.fairfaxcounty.gov/dta_taxevaders/AddRecord.aspx In fact, I've turned in tax evaders myself because they are, in effect, stealing from those of us that are law abiding citizens. I know those I've turned in have faced still fines and penalties and had to register their vehicles in Virginia.
Anyway, I hope this helps and good luck.