Rogue's new name for one working in theatre (7)
I believe the answer is:
surgeon
'one working in theatre' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'rogue's new name' is the wordplay.
'new' indicates an anagram.
'name' becomes 'n' (common abbreviation e.g. on forms).
'rogues' anagrammed gives 'surgeo'.
'surgeo'+'n'='SURGEON'
'for' is the link.
Can you help me to learn more?
(Other definitions for surgeon that I've seen before include "Theatre operator" , "Naval doctor" , "Sawbones" , "Physician" , "Theatre worker" .)