The most common and most likely answer to this crossword clue is the 9 letter word EXCHANGED
I've seen this crossword clue in Financial Times
E
X
C
H
A
N
G
E
D
Buddy explains!

The straight part
We know that "Swapped" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swapped = exchanged.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.
What does EXCHANGED mean?
EXCHANGED verb- To trade or barter.
- To replace with, as a substitute.