Your example code is close, just not quite there yet.

use strict;
use XML::Twig;

my $parser = new XML::Twig(
    twig_print_outside_roots => 1,
    twig_roots               => {
        'Title[@Name="Advanced Perl Programming"]' =>
            sub {
                my ( $tree, $element ) = @_;
                $element->set_att( Name => 'Advanced Perl' );
                $element->print;
            }
    }
);

$parser->parse_file('books.xml');
[download]

Notice a couple of things I did differently:
- Put your twig_roots key in single quotes. Since you're using a '@' to select an element with an attribute, you don't want Perl to think you're trying to throw a variable name in there.
- Rather than specifying your twig_roots value as a 1, use either a reference to a sub or an anonymous sub as I did above. This gives you a lot more flexibility to do what you want. Inside this sub, is where we want to change the "Name" attribute.
- Specify twig_print_outside_roots so that it prints the rest of the document along with the twig_root you've specified

That should do what you were attempting.

--Brian