Flexible new star learned to change characters (13)
I believe the answer is:
transliterate
'change characters' is the definition.
(to transliterate is to put into a different script)
'flexible new star learned' is the wordplay.
'flexible' is an anagram indicator (I've seen this in other clues).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'learned' becomes 'literate' (synonyms).
'n'+'star'='nstar'
'nstar' with letters rearranged gives 'trans'.
'trans'+'literate'='TRANSLITERATE'
'to' acts as a link.
(Other definitions for transliterate that I've seen before include "Write (word) in letters from another language - narrates title (anag)" , "Switch from one alphabet to another" , "Change into different alphabet" , "Put new letters in" , "Switch between alphabets" .)