The most common and most likely answer to this crossword clue is the 7 letter word CHANGED
I've seen this crossword clue in The Daily Telegraph
C
H
A
N
G
E
D
More clues leading to the result CHANGED
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 = changed.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 CHANGED mean?
CHANGED verb- To become something different.
- To make something into something else.
- To replace.
- To replace one's clothing.
- To replace the clothing of (the one wearing it).
- To transfer to another vehicle (train, bus, etc.)
- To exchange.
- To change hand while riding (a horse).