Do not change it boy - it's what John Wayne wore! (6,3)

'do' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'not change it boy it's what john wayne wore' is the wordplay.
I cannot really see how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'boy' could be 'bo' and 'bo' is found within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?