Driver may change into this kind of party clothing (5,4)

I believe the answer is:

third gear

'driver may change into this' is the definition.

'kind of party clothing' is the wordplay.
'kind of party' becomes 'third'.
'clothing' becomes 'gear' (I've seen this before**).
'third'+'gear'='THIRD GEAR'

I've seen this clue in The Guardian.

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