It's time to make contingency plans as the details of the post-Brexit import registration and documentation process will only be known after the UK and EU27 have agreed on their future relationship.
We suggest you develop contingencies to cover the various potential scenarios that could apply to import registration and documentation. One idea would be to compare current processes and procedures for imports from EU countries to the regulations that apply to imports from non-EU countries. This will help you to understand where changes may take place.