You're doing something else wrong then. This works just fine.

#!/usr/bin/env perl
use strict;
use warnings;

use XML::Twig ();

my $twig = XML::Twig->new;

$twig->parse( qq{<img src="/foo/bar.jpg" />\n} );

for my $img ( $twig->get_xpath( "//img" ) ) {
  $img->change_att_name( 'src', 'links' );
}

$twig->print;

exit 0;

__END__
## Outputs:
<img links="/foo/bar.jpg"/>
[download]