Forgive Charlie breaking old custom (6)
I believe the answer is:
excuse
'forgive' is the definition.
(excusing is a kind of forgiving)
'charlie breaking old custom' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'breaking' indicates putting letters inside.
'old' becomes 'ex'.
'custom' becomes 'use' (use is a kind of custom).
'ex'+'use'='exuse'
'c' put inside 'exuse' is 'EXCUSE'.
(Other definitions for excuse that I've seen before include "Upstanding community members" , "Pardon or justify" , "A self-justification" , "Absolve" , "Seek to justify (a fault)" .)