Obligatory change I urged — regret doing a U-turn (2,7)
I believe the answer is:
de rigueur
'obligatory' is the definition.
(similar in meaning)
'change i urged regret doing a u-turn' is the wordplay.
'change' indicates anagramming the letters.
'regret' becomes 'rue' (to rue something is to regret it).
'doing a u-turn' says the letters should be written backwards.
'rue' in reverse letter order is 'eur'.
'i'+'urged'='iurged'
'iurged' is an anagram of 'derigu'.
'derigu'+'eur'='DE RIGUEUR'
(Other definitions for de rigueur that I've seen before include "Required by strict etiquette or fashion (French)" , "necessary" , "Proper" , "Required by custom or etiquette" , "Strictly" .)