Cleansing rite to exercise some mercy on sovereign’s admission (7,8)

I believe the answer is:

smoking ceremony

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'exercise some mercy on sovereign's admission' is the definition.
I know nothing about this answer so I can't tell whether this works.

'cleansing rite' is the wordplay.
'cleansing' becomes 'smoking' (I am not sure about this - if you are sure you should believe this answer much more).
'rite' becomes 'ceremony' (I've seen this in another clue).
'smoking'+'ceremony'='SMOKING CEREMONY'

'to' is the link.

Can you help me to learn more?

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

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