One last change in a book (5)
I believe the answer is:
atlas
'a book' is the definition.
(atlas is a kind of book)
'one last change in' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'change' is an anagram indicator.
'in' indicates putting letters inside.
'last' anagrammed gives 'atls'.
'a' inserted within 'atls' is 'ATLAS'.
(Other definitions for atlas that I've seen before include "Size of paper once" , "Sky-toting Titan" , "I carry a huge weight" , "Sort of book" , "Mythological Titan (involved with the world of maps?)" .)