China seems to manage it easily enough for all the thousands of different products the EU imports from there.
Getting Nissan cars, for example, CE marked is easy - they already are. If and when Nissan make new models, or the EU changes its rules, it will be just as easy, and arguably easier, to get those cars CE marked in Sunderland as it will be in Japan, or any other non-EU country.
Of course, Nissan may decide to make them in Japan anyway. If there is a lasting global downturn in the car market, you'd expect manufacturers to consolidate their manufacture in their own home country.
If there's not a downturn, then, as always, car manufacturers will choose to manufacture in whichever country offers them the best deal. That may not be the cheapest place as they also consider things like stability and ease of relocation. Costs and projected profits are the main driving force, and any tariffs or other protectionist measures will need to be factored into the likely costs.