This does nearly what you want. Perhaps you can modify it to get what you want (but see my question below).

my %hash;
while ( <DATA> ) {
    chomp;
    my @elts = split /\|_\|/, $_;
    $hash{$elts[0]}->{$elts[1]} = $elts[2];
}

print Dumper \%hash;

__DATA__
200326951|_|rel_Access1|_|200315482|_|
200326951|_|rel_Access1|_|200315786|_|
200326951|_|rel_Access2|_|200315482|_|
200326951|_|rel_Access2|_|200315786|_|
[download]

Output:

$VAR1 = {
          '200326951' => {
                           'rel_Access2' => '200315786',
                           'rel_Access1' => '200315786'
                         }
        };
[download]

In your sample output, why does 'rel_Access2' => '200315786' but 'rel_Access1' => '200315482'?