To do so means I'm wrong in nominal usage (7)

I believe the answer is:

misname

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'to do so means i'm wrong in nominal usage' is the definition.
I can't judge whether this definition defines the answer.

'to do so means i'm wrong' is the wordplay.
'to do so' becomes 'm' (I am not sure about this - if you are sure you should believe this answer much more).
'i'm' becomes 'i' (I've seen this in other clues).
'wrong' indicates anagramming the letters.
'means'+'i'='meansi'
'meansi' anagrammed gives 'isname'.
'm'+'isname'='MISNAME'

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I've seen this clue in the Evening Standard.

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