Doctor sat in for matron for a change (14)

I believe the answer is:

transformation

'a change' is the definition.
(transformation is a kind of change)

'doctor sat in for matron' is the wordplay.
'doctor' indicates an anagram.
'sat'+'in'+'for'+'matron'='satinformatron'
'satinformatron' anagrammed gives 'TRANSFORMATION'.

'for' is the link.

(Another definition for transformation that I've seen is " Process of change".)

I've seen this clue in The Independent.

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