The most common and most likely answer to this crossword clue is the 4 plus 8 letter word ROLE REVERSAL
I've seen this crossword clue in The Guardian
R
O
L
E
R
E
V
E
R
S
A
L
More clues leading to the result ROLE REVERSAL
Buddy explains!
The straight part
We know that "Change in personal relations" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case change in personal relations = role reversal.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.