Loves having rewritten Act 5 in book (6)
I believe the answer is:
octavo
'book' is the definition.
(I've seen this before)
'loves having rewritten act 5' is the wordplay.
'loves' becomes 'oo'.
'having' is an insertion indicator.
'rewritten' indicates an anagram.
'5' becomes 'v' ('v' can be a synonym of '5').
'act'+'v'='actv'
'actv' is an anagram of 'ctav'.
'oo' enclosing 'ctav' is 'OCTAVO'.
'in' acts as a link.
(Other definitions for octavo that I've seen before include "An eight-leaved book or page" , "Size of a book, pages are made by folding a sheet of paper three times to form eight leaves (6)" , "Size of book page" , "Common book size" .)