Rewritten rule said to be remaining (8)
I believe the answer is:
residual
'be remaining' is the definition.
(I've seen this before)
'rewritten rule said' is the wordplay.
'rewritten' indicates anagramming the letters.
'rule'+'said'='rulesaid'
'rulesaid' with letters rearranged gives 'RESIDUAL'.
'to' acts as a link.
(Other definitions for residual that I've seen before include "Pertaining to what is left over" , "Left over as a remainder" , "'Remaining, left over (8)'" , "Leftover - used rail (anag)" , "Concerning what is left over" .)