I want that at the end $ref contains a reference to $ref->{baz}.

use Data::Dumper;
my $ref = { "baz" => [1,2,3,4] };
print Dumper $ref;
sub bazify {return $_[0]->{baz} };
$ref = bazify($ref);
print Dumper $ref;
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update: note that it is not a reference to $ref->{baz}, but its value (which is a ref to an anonymous array)