My engineering license issued by the CAA transitioned to EASA Part 66 smoothly and without any difficulties. The same for transitioning to a EASA ATPL.With respect, nor did you see anything which definitely assured that they would. There needs to be agreements in place, which may not be the case,in order to ensure that there is a seamless transition. At its worst, it could mean that aircraft maintenance mechanics who are still as competent on April 1st , as they were the preceding Friday, will no longer be authorised to sign off on a repair. There needs to be mutual recognition agreements signed off . These can be done even pro tempore, but it needs to have happened now.
I trust that you would not conduct your own business on such a hope basis. You presumably would require an audit trail of permissions and validated procedures from authorised bodies.
Crew & engineering licensing in EU member states was never anywhere near the high standards set by the U.K. CAA. That’s why much of the EASA legislation is imported from U.K. practices and procedures and why transition to EASA licensing is do easy.
Rest assured U.K. pilots and U.K. aircraft engineers will continue to operate throughout the EU after Brexit day. The U.K. standard is the gold standard that the EU aspired to. It won’t be a problem.