Article changing entire racecourse (7)
I believe the answer is:
aintree
'racecourse' is the definition.
(horseracing venue in Liverpool)
'article changing entire' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'changing' indicates anagramming the letters.
'entire' anagrammed gives 'intree'.
'a'+'intree'='AINTREE'
(Other definitions for aintree that I've seen before include "Liverpool's racecourse" , "Venue of the Grand National race" , "National racecourse" , "Here they run" , "Merseyside racecourse" .)