depends on what licence you have
if you have a ppl, no it can't
if you have nppl m, ie microlight licence, and you wish to fly an sep machine
ie under 2 ton, you can simply add your hours, + you need 5 further hours training on an sep ( minimum ) and take another exam principals of flight
all the already taken exams do not need to be retaken.
the only draw back at present, is, the nppl sep licence can only be used in the UK, whereas you can fly within Europe with the nppl m