This rogue could become so upstanding (9)
I believe the answer is:
righteous
'upstanding' is the definition.
(thesaurus)
'this rogue could become' is the wordplay.
'could become' indicates an anagram.
'this'+'rogue'='thisrogue'
'thisrogue' is an anagram of 'RIGHTEOUS'.
'so' acts as a link.
(Other definitions for righteous that I've seen before include "Good!" , "Showing virtue" , "Morally justified" , "Virtuous, free from sin or guilt" , "law-abiding" .)