Modify it with a relevant option (11)
I believe the answer is:
alternative
'option' is the definition.
('alternative' can be a synonym of 'option')
'modify it with a relevant' is the wordplay.
'modify' indicates an anagram (I've seen this in other clues).
'with' says to put letters next to each other.
'a'+'relevant'='arelevant'
'it' after 'arelevant' is 'arelevantit'.
'arelevantit' anagrammed gives 'ALTERNATIVE'.
(Other definitions for alternative that I've seen before include "Available as another possibility" , "choice between 2" , "(Of two things) mutually exclusive" , "One of two or more available possibilities" , "One possible option" .)