Planet needing to change yen in abundance (7)
I believe the answer is:
aplenty
'in abundance' is the definition.
(I've seen this before)
'planet needing to change yen' is the wordplay.
'needing to change' indicates anagramming the letters (I've seen 'needs to change' mean this).
'yen' becomes 'y' (resembles the symbol for the currency of Japan).
'planet' with letters rearranged gives 'aplent'.
'aplent'+'y'='APLENTY'
(Other definitions for aplenty that I've seen before include "heaps" , "more than enough" , "by the score" , "lots of it" , "In abundance" .)