Substitute is right over upturned label inside safe (9)
I believe the answer is:
surrogate
'substitute' is the definition.
(I know that substitute can be written as surrogate)
'right over upturned label inside safe' is the wordplay.
'right over' becomes 'ro' (this could be a standard abbreviation I've not previously seen).
'upturned' says the letters should be written in reverse.
'label' becomes 'tag' (tag is a kind of label).
'inside' indicates putting letters inside.
'safe' becomes 'sure' (both can mean secure).
'tag' backwards is 'gat'.
'ro'+'gat'='rogat'
'rogat' put into 'sure' is 'SURROGATE'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for surrogate that I've seen before include "Deputising substitute" , "Argues about rot with substitute or deputy" , "stand-in" , "(A) substitute in office" , "One standing in" .)