Change voice briefly in front of the Queen (5)
I believe the answer is:
alter
'change' is the definition.
('alter' can be a synonym of 'change')
'voice briefly in front of the queen' is the wordplay.
'voice' becomes 'alto' (alto is a kind of voice).
'briefly' means to remove the last letter.
'in front of' means one lot of letters go next to another.
'the queen' becomes 'er' (Elizabeth Regina).
'alto' with its final letter taken off is 'alt'.
'alt'+'er'='ALTER'
(Other definitions for alter that I've seen before include "Bout of extravagant spending" , "Amend" , "Change, maybe later" , "shift" , "Make changes to" .)