Tamper with retro piece of religious iconography outside court (6)
I believe the answer is:
doctor
'tamper with' is the definition.
(thesaurus)
'retro piece of religious iconography outside court' is the wordplay.
'retro' is a reversal indicator (retro is Latin for 'backwards').
'piece of religious iconography' becomes 'rood' (term for a crucifix).
'outside' is an insertion indicator.
'court' becomes 'ct' (abbreviation used in road names).
'rood' in reverse letter order is 'door'.
'door' going around 'ct' is 'DOCTOR'.
(Other definitions for doctor that I've seen before include "GP" , "One treats the ill" , "An apple a day keeps him away" , "Spike?" , "Falsify; quack" .)