Unidentified current coin got replaced (9)
I believe the answer is:
incognito
'unidentified' is the definition.
(thesaurus)
'current coin got replaced' is the wordplay.
'current' becomes 'in' ('in' can mean current or trendy).
'replaced' indicates an anagram.
'coin'+'got'='coingot'
'coingot' anagrammed gives 'cognito'.
'in'+'cognito'='INCOGNITO'
(Other definitions for incognito that I've seen before include "Camouflaged" , "With one's identity concealed" , "Using false name" , "as disguised person appears?" , "appear unidentifiable" .)