package My::Utils;

my %instance;

sub read_conf {
  #fills %instance
}

sub value {
  my ($name, $new_val) = @_;
  if (2 == @_) { #new value passed
    $instance{$name} = $new_val;
  }
  return $instance{$name};
}

package My::Something
use My::Utils;
print My::Utils::value("something_configured");