Shorten can manage head count in the gallery (8)
I believe the answer is:
truncate
'shorten' is the definition.
(I know that truncate is a type of shorten)
'manage head count in the gallery' is the wordplay.
'manage' becomes 'run' (both can mean to organise).
'head' suggests taking the first letters.
'in the' is an insertion indicator.
'gallery' becomes 'tate' (Tate Modern, Tate Britain etc).
The first letter of 'count' is 'c'.
'run'+'c'='runc'
'runc' placed into 'tate' is 'TRUNCATE'.
'can' acts as a link.
(Other definitions for truncate that I've seen before include "Make shorter by cutting off" , "Lop" , "Dock" , "Shorten by cutting off the top" , "Cut short" .)