Before midday object to change (5)
I believe the answer is:
amend
'change' is the definition.
(amending is a kind of changing)
'before midday object' is the wordplay.
'before midday' becomes 'am'.
'object' becomes 'end' (I've seen this in other clues**).
'am'+'end'='AMEND'
'to' acts as a link.
(Other definitions for amend that I've seen before include "Rectify" , "Make minor improvements to (something)" , "Correct or alter to improve" , "Make small changes to" , "Make corrections to (eg, document)" .)