When there's some lack of variety, make a change (4)

I believe the answer is:

vary

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'a change' is the definition.
(I know that change can be written as vary)

I don't understand the rest of the clue.

(Other definitions for vary that I've seen before include "Differ from a standard" , "Differ, alter" , "Modulate" , "Diversify" , "Differ in size" .)

I've seen this clue in the Evening Standard.

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