Code of honour an ex-president papers over (7)
I believe the answer is:
bushido
'code of honour' is the definition.
(I've seen this before)
'an ex-president papers over' is the wordplay.
'an ex-president' becomes 'Bush' (either of the George Bushes).
'papers' becomes 'ID' (identifying documents are one's 'papers').
'over' becomes 'o' (cricket abbreviation).
'bush'+'id'+'o'='BUSHIDO'
(Other definitions for bushido that I've seen before include "Fighters' code" , "Code for old military" , "Japanese code of chivalry" , "honourable code" , "Strict ethical code of Japanese samurai" .)