Crossword Genius

Leader having been deposed, insurrectionist changing (12)

Ross

I believe the answer is:

evolutionary

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'changing' is the definition.
Although both the answer and definition are adjectives, I don't see how one could define the other.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Another definition for evolutionary that I've seen is " Gradually developing".)

I've seen this clue in The Times.
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