my $orig = 'doc.xml';
use autodie 1.999;
use POSIX 'strftime';

my $back = $orig . strftime( '-%Y-%m-%d', localtime );
rename $orig, $back;

open my $newfh, '>', $orig;

my $t = XML::Twig->new(
    twig_roots => {
        'qpass:merchant' => sub {
            my ( $t, $price ) = @_;
            {
                my $ra = $price->text;
                $ra =~ s/_/ /g;
                $price->set_text($ra);
            }
            $price->print($newfh);
        },
    },
    twig_print_outside_roots => $newfh,
);
$t->parsefile($back);
$t->flush;    #don't forget
undef $t;     #
close $newfh;