Left regent to change spectacles (9)
I believe the answer is:
lorgnette
'spectacles' is the definition.
(lorgnette is a kind of spectacles)
'left regent to change' is the wordplay.
'left' becomes 'l' (common abbreviation).
'change' indicates anagramming the letters.
'regent'+'to'='regentto'
'regentto' with letters rearranged gives 'orgnette'.
'l'+'orgnette'='LORGNETTE'
(Other definitions for lorgnette that I've seen before include "Pair of spectacles on a stick" , "Device helping to read" , "Pair of spectacles on a long handle" , "Pair of spectacles on ling handle" , "Opera glass" .)