Complex sentence: While the Beatles were unaware of this announcement, Epstein had already declined the invitation when they were in Tokyo, in keeping with his policy since 1964 regarding all embassy or other official functions to which the group were often invited while on tour.
Split into simpler sentences: While the Beatles were unaware of this announcement, Epstein had already declined the invitation when they were in Tokyo. This was in keeping with his policy since 1964 regarding all embassy or other official functions to which the group were often invited while on tour.