Eventually change to total slang (2,4,4)
I believe the answer is:
at long last
'eventually' is the definition.
(I've seen this before)
'change to total slang' is the wordplay.
'change to' indicates an anagram.
'total'+'slang'='totalslang'
'totalslang' anagrammed gives 'AT LONG LAST'.
(Other definitions for at long last that I've seen before include "repairing the biggest shoes?" , "producing larger shoes?" , "Where cobbler dealing with size 12 shoes will be" , "cobbling size seventeens?" , "Finally" .)