Am the finisher and modifier (7)

I believe the answer is:

amender

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'modifier' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?

'am the finisher' is the wordplay.
'the finisher' becomes 'ender' (I've seen this in another clue).
'am'+'ender'='AMENDER'

'and' acts as a link.

Can you help me to learn more?

(Other definitions for amender that I've seen before include "Editor" , "agent of change" .)

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

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