Yankee altering work on venue? It might happen (3,5,4)
I believe the answer is:
you never know
'it might happen' is the definition.
(phrase used to say something might happen)
'yankee altering work on venue?' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'altering' is an anagram indicator.
'work'+'on'+'venue'='workonvenue'
'workonvenue' anagrammed gives 'ouneverknow'.
'y'+'ouneverknow'='YOU NEVER KNOW'
(Other definitions for you never know that I've seen before include "perhaps" , "lt's possible" , "One can't predict the future, or can one?" .)