Noticeably different leading actor in TV role (3,5)
I believe the answer is:
set apart
'noticeably different' is the definition.
(that which is set apart from the rest)
'leading actor in tv role' is the wordplay.
'leading' indicates taking the first letters.
'in' is an insertion indicator.
'tv' becomes 'set' (I've seen this in other clues).
'role' becomes 'part' (synonyms).
The initial letter of 'actor' is 'a'.
'set'+'part'='setpart'
'a' inserted within 'setpart' is 'SET APART'.
(Other definitions for set apart that I've seen before include "reserved" , "Keep separate (for a special purpose)" , "singled out" , "Isolate" , "specially allocated" .)