OK, it's really late for an answer here, but here is the XML::Twig script that does it. It's a little simpler than the regexp one and certainly a lot more robust.

#!/bin/perl -w
use strict;
use XML::Twig;

my( $main_file, $upd_file)= @ARGV;

# get the info we need by loading the update file
my $t_upd= new XML::Twig();
$t_upd->parsefile( $upd_file);

my $upd_badge_id = $t_upd->root->next_elt( 'badge_id')->text;
my $upd_chore    = $t_upd->root->next_elt( 'jobs');

# now process the main file
my $t= new XML::Twig( TwigHandlers => { jobs => \&jobs, },
		      PrettyPrint => 'indented',
		    );
$t->parsefile( $main_file);
$t->flush;           # don't forget or the last closing tags won't be printed

sub jobs
  { my( $t, $jobs)= @_;
    # just replace jobs if the previous badge_id is the right one
    if( $jobs->prev_elt( 'badge_id')->text eq $upd_badge_id)
      { $upd_chore->replace( $jobs); }
    $t->flush;    # print and flush memory so only one job is in there at once
  }