If you can do all your exams before training overseas, good luck and best wishes.
But just think about where you will take the exams. They have to be taken at a RF or FTO. If all the RF does is Groundschool, probably no problem. But if the RF is also struggling to find customers who want to learn to fly there - and discovers you want to sit the exams so you can nip off Stateside to an intensive PPL place, how keen do you think they'll be on you?
I offer my customers free exams if they train at my RF as a structured part of the course. However, if they want to do just the exams before going overseas to train cheaper then they will have to pay the same rates as the CAA charge.