Looks like doubling down though the letter also potentially provides an exit route. You'd hope the UK government have thought this through, for although there is no specific right for the EU to have an office in the agreement, they have plenty of other rights. 
Timing-wise when you've started one set of major trade talks and are about to start others including with the US, not shy of expressing opinions on Ireland, is an odd time to suggest that you intend to take a literalist approach to international agreement text.
This as well. Now the EU were the first to make a Belfast office a public issue. So both sides are raising tensions. Behind this there are serious concerns in many EU Member States about whether the UK can be trusted (shared by some outside the EU).
We return to those serious choices the UK government faces in the months to come. Do they want trade deals with EU and US? Will they implement the Northern Ireland protocol checks the PM has denied? All to decide in the midst of a pandemic... prospectmagazine.co.uk/economics-and-…
