Change position of back row (9)
I believe the answer is:
rearrange
'change position of' is the definition.
(I've seen this before)
'back row' is the wordplay.
'back' becomes 'rear' (something's rear is its back).
'row' becomes 'range' (range can mean a row or chain of things).
'rear'+'range'='REARRANGE'
(Other definitions for rearrange that I've seen before include "Move to new positions" , "Give another order" , "Again work out" , "Change the position of" , "What 8 [ADJUSTER] may do" .)