Yes, The euro cars have different accessories and engines.
You can retrofit Euro parts on the US Focus with little or no modification.
It all depends on what you buy.
If you decide you want to get a Euro part, you should do some research to see if anyone has installed a particuar Euro part on a US Focus so you don't have to figure it out yourself if someone has already done it.
European-parts.net is a good place to get parts. I suggest buying more than one item to justify the shipping cost.