When I've done mass changes of DNS serial numbers, I've tended to use an in place replacement such as:

`perl -pi -e 's/2007\d\d\d\d\d\d/2007102901/' *.com`
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and repeat it for the other zone types. The serial number in 'date format' is unique enough that it's just not found anywhere else in the zone files I manage.

Otherwise, moritz's suggestion of a template seems to fit your needs quite well.

Update: To check for an appropriate serial number, something like the code below could be useful:

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

#
# warning - untested code.
# Let's find the largest serial number of the lot.
#

my $patt = qr{200\d{7}};
my $dns_zones = '/etc/named/primary/';
# chdir $dns_zones or die "Cannot enter zone file directory.\n";
my @zones = split /\n/, `ls -1`;
my $curr_time = get_serial_number();
for my $z (@zones) {
    open (ZONE, "<", $z) or 
        die("Cannot open zone file $z.\n");
    while(<ZONE>) {
#
# I habitually follow the serial # with a space, a semicolon, a space
# and the word 'serial'
#
        if ( /($patt)\s+\;\s+serial/ ) {
            my $serial = $1;
            $curr_time = ++$serial if ( $serial > $curr_time );
            last;
        }
    }
    close(ZONE);
}
print "Final time = $curr_time\n";
#
# replace in place here.
#
sub get_serial_number {
    my @time = localtime();
    my $day   = substr("0" . $time[3], -2 );
    my $month = $time[4] + 1;
    my $year = 1900 + $time[5];
    return $year . $month . $day . "01";
}
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