Grandly taking over diocese at end of this month (2,5)
I believe the answer is:
Here is my best explanation:
'grandly' is the definition.
'over diocese at end of this month' is the subsidiary indication.
'over' says the letters should be written backwards.
'diocese' becomes 'ely' (I've seen this before).
'at end of' is a charade indicator (letters next to each other).
'this month' becomes 'inst' (I've seen this before**).
'ely' written backwards gives 'yle'.
'yle' after 'inst' is 'instyle'.
'taking' is the link.
(Other definitions for in style that I've seen before include "A la mode", "With a grand manner", "(Done) with a grand manner", "In a grand manner", "with panache" and "emphatically".)