Recently I had to solve similar task so maybe my solution will help you. I created singleton class, which loads YAML file during initialisation and every time you requesting structure it checks if file was changed, and reloading it if needed. Example code is follows, I would like to get any comments:

package YAMLReload;
use MooseX::Singleton;
use namespace::autoclean;
use YAML qw(LoadFile);

has _fname => ( is => 'ro', default => '/path/to.yml' );
has _tree  => ( is => 'rw' );
has _mtime => ( is => 'rw' );
has _checked => ( is => 'rw', default => sub { time } );

sub BUILD {
    my $self = shift;
    $self->_reload_tree;
}

sub _reload_tree {
    my $self = shift;
    $self->_mtime( ( stat( $self->_fname ) )[9] );
    $self->_tree( LoadFile( $self->_fname ) );
}

sub _check {
    my $self = shift;
    return if time - $self->_checked < 10;
    $self->_checked(time);
    return if $self->_mtime == ( stat( $self->_fname ) )[9];
    $self->_reload_tree;
}

sub get_tree {
    my $self = shift;
    $self->_check;
    return $self->_tree;
}

no Moose;
__PACKAGE__->meta->make_immutable;
1;
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