Thanks for all the info above!
I summarized here the complete procedure for my system (RH9), hopefully it can save some time for someone else.
# as root:
# check the old time zone info
zdump -v /etc/localtime | grep 2007
# shows:
#/etc/localtime Sun Apr 1 09:59:59 2007 UTC = Sun Apr 1 01:59:59 2007 PST isdst=0 gmtoff=-28800
#/etc/localtime Sun Apr 1 10:00:00 2007 UTC = Sun Apr 1 03:00:00 2007 PDT isdst=1 gmtoff=-25200
#/etc/localtime Sun Oct 28 08:59:59 2007 UTC = Sun Oct 28 01:59:59 2007 PDT isdst=1 gmtoff=-25200
#/etc/localtime Sun Oct 28 09:00:00 2007 UTC = Sun Oct 28 01:00:00 2007 PST isdst=0 gmtoff=-28800
service ntpd stop
# use a tmp directory
mkdir -p tzone ; cd tzone
# get the new timezone info
wget
ftp://elsie.nci.nih.gov/pub/tzdata2007c.tar.gz
tar xzf tzdata2007c.tar.gz
# adjust the system's zoneinfo
zic -d /usr/share/zoneinfo/ northamerica
# re-run redhat date config tool
redhat-config-date
# just confirm my timezone is America/Los-Angeles Pacific Time
# check that the change has taken place
zdump -v /etc/localtime | grep 2007
# shows (to my satisfaction):
#/etc/localtime Sun Mar 11 09:59:59 2007 UTC = Sun Mar 11 01:59:59 2007 PST isdst=0 gmtoff=-28800
#/etc/localtime Sun Mar 11 10:00:00 2007 UTC = Sun Mar 11 03:00:00 2007 PDT isdst=1 gmtoff=-25200
#/etc/localtime Sun Nov 4 08:59:59 2007 UTC = Sun Nov 4 01:59:59 2007 PDT isdst=1 gmtoff=-25200
#/etc/localtime Sun Nov 4 09:00:00 2007 UTC = Sun Nov 4 01:00:00 2007 PST isdst=0 gmtoff=-28800
# force ntp to adjust the clock, even if there was a large gap:
ntpdate clock.redhat.com
# make sure ntpd will be restarted after reboot
chkconfig ntpd on
# restart ntpd now
service ntpd start