Late modification if rotter is reformed (8)

I believe the answer is:

retrofit

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'late modification if rotter is reformed' is the definition.
I can't tell whether this definition defines the answer.

'if rotter is reformed' is the wordplay.
'is reformed' is an anagram indicator.
'if'+'rotter'='ifrotter'
'ifrotter' with letters rearranged gives 'RETROFIT'.

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(Other definitions for retrofit that I've seen before include "Fit with accessory not on original" , "Modification made after manufacture" , "Belatedly modify" , "make change after delivery" , "Make later modifications to (equipment, etc)" .)

I've seen this clue in the Sydney Morning Herald.

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