Here's an idea: Using EASA drafted, previously agreed contracts, agreements and legislation change the title at the head of the relevant document to whatever you want to call it.
There it is, solved !
No it's not, well not in the commercial world. Just for the sake of it an outlandish what if: Imagine you need to carry a piece of paper on your aircrfat saying the widgets that hold your wings on have been checked by a EASA department in Munich to ensure they conform to a certain standard and that same department in Munich is responsible for ensuring continued compliance..
BREXIT Day :....EASA gets crossed out, UK CAA gets inked in.
Brexit Day plus a week or so - You get ramp checked in the States, your widget paperwork is examined, your friendly FAA man looks at the amended paperwork and asks " it says UK CAA here , where in the UK now are your widgets checked for continued compliance..... "