Changes tack about half-open overlays (7)
I believe the answer is:
veneers
'overlays' is the definition.
(I've seen this in another clue)
'changes tack about half-open' is the wordplay.
'changes tack' becomes 'veers' (I am not sure about this - if you are sure you should believe this answer much more).
'about' indicates putting letters inside.
'half' indicates taking half.
'open' with half the letters taken is 'en'.
'veers' going around 'en' is 'VENEERS'.
Can you help me to learn more?
(Other definitions for veneers that I've seen before include "Thin wooden sheets" , "Coatings of a thin layers of superior quality" , "Fine wood facings" , "Superficial overlays" .)