I tried to use the guide on http://cookbook.soaplite.com/#changing%20method%20name%20in%20response , but it doesn't seem to work, I guess it's not applicable on what I'm doing.

The code you posted doesn't show any code from the guide, or a client.

It works for me, goes from

<product_info_requestResponse xmlns="http://127.0.0.1/MyModule" xsi:ni
+l="true"/>
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<product_info_request xmlns="http://127.0.0.1/MyModule">
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#!/usr/bin/perl --
#~ 2011-08-24-07:25:06PDT by Anonymous Monk
#~ perltidy -csc -otr -opr -ce -nibc -i=4     
use strict;
use warnings;
use Proc::Background;

Main( @ARGV );
exit( 0 );

sub Main {
    my( $cos ) = @_;
    if( $cos ){
        GoServer() if $cos == 1;
        GoClient() if $cos == 2;
    } else {
        GoGo();
    }
}

sub GoGo {
    my $serv = Proc::Background->new( $^X, __FILE__, 1 => 'GoServer' )
+;
    sleep 1;
    my $cli = Proc::Background->new( $^X, __FILE__, 2 => qw'Go Client'
+ );
    sleep 1;
    $cli->die;
    $serv->die;
}

sub GoServer {    
    require MyModule;
    require SOAP::Lite;
    require SOAP::Transport::HTTP;
    my $daemon = SOAP::Transport::HTTP::Daemon->new(
        LocalAddr => '127.0.0.1',
        LocalPort => 1203,
        Reuse     => 1
    )
#~     ->serializer( MySerializer->new ) # WORKS
    ->dispatch_to('MyModule');
    
    print "SOAP server started at ", $daemon->url, "\n";
    $daemon->handle;
}    

sub GoClient {
    require SOAP::Lite;
    my $soap = SOAP::Lite
        -> uri('http://127.0.0.1/MyModule')
        -> proxy('http://127.0.0.1:1203');
    $soap->transport->add_handler("request_send",  \&pp_dump );
    $soap->transport->add_handler("response_done", \&pp_dump );
    $soap->product_info_request("one","two","three");
}


sub pp {
    use XML::Twig;
    open my($fh), '>', \my $str;
    no warnings 'newline';
    XML::Twig->new(qw! pretty_print record !)->xparse(@_)->print( $fh 
+);
    return $str;
}

sub pp_dump {
    my $content = $_[0]->content('');
    $_[0]->content( pp($content) );
    print $_[0]->as_string,"\n";
    return;
}


BEGIN {
    package MyModule;
    use strict;
    sub product_info_request
    {
        my ($self,@args) = @_;
    
        return (SOAP::Header->name(prod_no => $args[1])->type('string'
+));
    }
    BEGIN { $INC{'MyModule.pm'} = __FILE__; }
    1;
}
BEGIN {
    package MySerializer;
    @MySerializer::ISA = 'SOAP::Serializer';
    sub envelope {
        $_[2] =~ s/Response$// if $_[1] =~ /^(?:method|response)$/;
        shift->SUPER::envelope(@_);
    }
    BEGIN { $INC{'MySerializer.pm'} = __FILE__; }
    1;
}

__END__
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