Importing yacht into the UK post Brexit

[Exmoor]

I have a 1992 Catalina 42 built in USA, and wish to bring it back to the UK next year,
How will the EU Certificate of conformity affect the import as we will no longer be in the EU
At the moment as I have a 1994 Yanmar 4JHE engine installed in the boat the regulation say that this engine will not pass emissions due to age irrespective of condition, so no cert of conformity so no import unless I buy a new engine

Will this change post Brexit?