Looking for the catch I searched the OP for any references to threads or forks. In the absence of a multiprocess environment I don't see the problem, e.g.:

my $href = \%hash;
my $aref = [];
@$aref = keys %hash;
for ( my $i = 0; $i <= $#$aref; $i++ ) {
    # do something with $href -> { $aref -> [$i ] }
    $href -> { $aref -> [$i] }{ XYZ }{ _callback } ( $href, $aref, $i 
+);
    # do more with $href -> { $aref -> [$i] }
}
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