Film theatre replaces variable, new projector (7)
I believe the answer is:
lantern
'projector' is the definition.
(as in a magic lantern projector)
'film theatre replaces variable new' is the wordplay.
I cannot quite understand how this works, but
'theatre' could be 'nt' (National Theatre) and 'nt' is located in the answer.
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is found within the answer.
The remaining letters 'laer' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for lantern that I've seen before include "Light in a protective casing" , "Light in a transparent protective case" , "Portable light source" , "Enclosed lamp" , "It illuminates" .)