A nicely matched couple (6)

I believe the answer is:

evened

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'matched couple' is the definition.
The answer and definition can be both related to change as well as being past participle verbs.
Maybe they are linked in a way I don't understand?

I don't understand the remainder of the clue.

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(Other definitions for evened that I've seen before include "Levelled" , "Made smooth and regular" , "Made level" , "Made smooth or equalised" .)

I've seen this clue in the Evening Standard.

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