Change direction of film that lacks heart (4)
I believe the answer is:
veer
'change direction' is the definition.
(to veer is to change direction suddenly)
'film that lacks heart' is the wordplay.
'film' becomes 'veneer' (both can mean an outer covering).
'that lacks heart' says to hollow out the word (remove centre letters) (I've seen 'lacking heart' mean this).
'veneer' with its middle taken out is 'VEER'.
'of' is the link.
(Other definitions for veer that I've seen before include "Change direction or course, like wind" , "Sudden direction change" , "Swing around" , "Swerve" , "Deviate" .)