What actor must do to appear as regular soldier (9)
I believe the answer is:
conscript
'regular soldier' is the definition.
(someone conscripted as a soldier)
'what actor must do to appear' is the wordplay.
I cannot quite see how this works, but
'do' could be 'con' (both can mean to defraud) and 'con' is found within the answer.
The remaining letters 'script' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'as' acts as a link.
(Other definitions for conscript that I've seen before include "Enrol for compulsory service" , "Enlist compulsorily" , "Person drafted into military service" , "One enrolled" , "One who hasn't volunteered" .)