Formally cancels as little brother gets into marbles (9)

I believe the answer is:

abrogates

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'formally cancels' is the definition.
I can't tell whether this defines the answer.

'little brother gets into marbles' is the wordplay.
'little brother' becomes 'bro'.
'gets into' indicates putting letters inside.
'marbles' becomes 'agates' (I've seen this in another clue).
'bro' inserted within 'agates' is 'ABROGATES'.

'as' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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