Am actor changing musical direction (7)
I believe the answer is:
marcato
'musical direction' is the definition.
(musical direction meaning with emphasis)
'am actor changing' is the wordplay.
'am' becomes 'ma' ('MA' can be a synonym of 'am').
'changing' indicates anagramming the letters.
'actor' is an anagram of 'rcato'.
'ma'+'rcato'='MARCATO'
(Other definitions for marcato that I've seen before include "strongly accented" , "Played with emphasis (music)" , "Emphatic" .)