The most common and most likely answer to this crossword clue is the 8 plus 3 letter word ALTERING (A)
I've seen this crossword clue in The Guardian
A
L
T
E
R
I
N
G
(
A
)
Buddy explains!
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.