Definite about changing nice and easy position needing little effort (8)
I believe the answer is:
sinecure
'easy position needing little effort' is the definition.
(term for a lucrative but easy job)
'definite about changing nice' is the wordplay.
'definite' becomes 'sure' (synonyms).
'about' means one lot of letters goes inside another.
'changing' indicates an anagram.
'nice' anagrammed gives 'inec'.
'sure' enclosing 'inec' is 'SINECURE'.
'and' acts as a link.
(Other definitions for sinecure that I've seen before include "A job that pays well for little work" , "Paid job involving little or no work" , "Very lucrative post" , "position needing little effort" , "Job for easy money" .)