I can sum up the rationale for the swapping in 3 letters - ESG. There is no good reason - just that. And no, there's no other movie or book source. I won't spoil the ending in case you do manage to see it, but if you do any research you'll quickly find out who is the perpetrator which may ruin enjoyment of the movie as it is a 'mystery'. (I solved it about 10 minutes in though)

I can some up the rationale for the swapping in 3 letters - ESG. There is no good reason - just that. And no, there's no other movie or book source. I won't spoil the ending in case you do manage to see it, but if you do any research you'll quickly find out who is the perpetrator which may ruin enjoyment of the movie as it is a 'mystery'. (I solved it about 10 minutes in though)