Has a change of heart re fast topspinners (7)

I believe the answer is:

relents

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'has a change of heart' is the definition.
I can't judge whether this defines the answer.

're fast topspinners' is the wordplay.
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'topspinners' becomes 's' (I can't explain this - if you can you should believe this answer much more).
're'+'lent'+'s'='RELENTS'

Can you help me to learn more?

(Other definitions for relents that I've seen before include "Comes round" , "Shows mercy" , "Eases off" , "is slackening" , "Becomes less severe and more lenient" .)

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

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