Bottom line leading to change (9)
I believe the answer is:
rearrange
'to change' is the definition.
(I've seen this before)
'bottom line leading' is the wordplay.
'bottom' becomes 'rear' (synonyms).
'line' becomes 'range' (I've seen this before).
'leading' means one lot of letters go next to another.
'rear'+'range'='REARRANGE'
(Other definitions for rearrange that I've seen before include "Tidy up" , "Change the position of" , "Sort" , "Make an anagram of" , "Move around" .)