Regulations initially one changes, covering fifty competitions (9)

I believe the answer is:

rivalries

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'competitions' is the definition.
('rivalry' can be a synonym of 'competition')

'regulations initially one changes covering fifty' is the wordplay.
'regulations initially' becomes 'ri' (this might be a standard abbreviation which I don't know about).
'one changes' becomes 'varies' (I've seen this before).
'covering' means one lot of letters goes inside another.
'fifty' becomes 'l' ('L' can be a synonym of 'fifty').
'varies' going around 'l' is 'valries'.
'ri'+'valries'='RIVALRIES'

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I've seen this clue in The Telegraph.

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