The lines

my @arr1 = @{$r1};
my @arr2 = @{$r2};
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are derefencing the array references, and making copies of them. You are then in turn modifying the local copy of the array.
Modifying it using

$r2->[1] = "q";
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should do the trick.

Update: $$r2[1] = "q"; will also work. It is your preference.