Moderates, as is one's wont, changing key in it (5,4)

'moderates' is the definition.
('tone down' can be a synonym of 'moderate')

'is one's wont changing key in it' is the wordplay.
I cannot quite see how this works, but
'one's' could be 'ones' and 'ones' is found within the answer.
'key' could be 'd' (musical key) and 'd' is found in the answer.
an anagram of 'wont' is 'town' which is located in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).

'as' is the link.

Can you help me to learn more?