CentOS 4 offers both yum and up2date to do updates of the operating system. You can use either or both of these to manage your updates.
Prior to using yum, you must import the RPM-GPG-KEY for CentOS-4 like this
rpm --import /usr/share/doc/centos-release-4/RPM-GPG-KEY
The following files are changed from the upstream RPMS. All changes are trademark and look/feel related unless otherwise noted under the specific RPM.anaconda-10.1.1.19-1.centos4.i386.rpm
anaconda-help-10.1.0-1.centos4.noarch.rpm
anaconda-product-4.0-2.centos4.noarch.rpm
anaconda-runtime-10.1.1.19-1.centos4.i386.rpm
createrepo-0.4.2-1.noarch.rpm
centos-release-4-1.2.i386.rpm
centos-yumconf-4-4.2.noarch.rpm
dhclient-3.0.1-12_EL.centos4.i386.rpm
dhcp-3.0.1-12_EL.centos4.i386.rpm
dhcp-devel-3.0.1-12_EL.centos4.i386.rpm
firefox-1.0.4-1.4.1.centos4.i386.rpm
firstboot-1.3.39-2.centos4.noarch.rpm
glade2-2.6.0-1.centos4.i386.rpm
gnome-desktop-2.8.0-3.centos4.i386.rpm
gnome-desktop-devel-2.8.0-3.centos4.i386.rpm
gnome-session-2.8.0-5.centos4.i386.rpm
httpd-2.0.52-12.ent.centos4.i386.rpm
httpd-devel-2.0.52-12.ent.centos4.i386.rpm
httpd-manual-2.0.52-12.ent.centos4.i386.rpm
httpd-suexec-2.0.52-12.ent.centos4.i386.rpm
indexhtml-4-1.centos4.noarch.rpm
initscripts-7.93.13.EL-2.centos4.i386.rpm
mod_perl-1.99_16-4.centos4.i386.rpm
mod_perl-devel-1.99_16-4.centos4.i386.rpm
mod_ssl-2.0.52-12.ent.centos4.i386.rpm
mozilla-1.7.8-1.4.1.centos4.i386.rpm
mozilla-chat-1.7.8-1.4.1.centos4.i386.rpm
mozilla-devel-1.7.8-1.4.1.centos4.i386.rpm
mozilla-dom-inspector-1.7.8-1.4.1.centos4.i386.rpm
mozilla-js-debugger-1.7.8-1.4.1.centos4.i386.rpm
mozilla-mail-1.7.8-1.4.1.centos4.i386.rpm
mozilla-nspr-1.7.8-1.4.1.centos4.i386.rpm
mozilla-nspr-devel-1.7.8-1.4.1.centos4.i386.rpm
mozilla-nss-1.7.8-1.4.1.centos4.i386.rpm
mozilla-nss-devel-1.7.8-1.4.1.centos4.i386.rpm
redhat-artwork-0.120-1.1E.centos4.1.i386.rpm
redhat-logos-1.1.25-1.centos4.3.noarch.rpm
rhn-applet-2.1.17-5.centos4.1.i386.rpm
squirrelmail-1.4.3a-9.EL4.centos4.noarch.rpm
system-config-printer-0.6.116-1.centos4.1.i386.rpm
system-config-printer-gui-0.6.116-1.centos4.1.i386.rpm
thunderbird-1.0.2-1.4.1.centos4.i386.rpm
up2date-4.4.5.6-2.centos4.2.i386.rpm
up2date-gnome-4.4.5.6-2.centos4.2.i386.rpm
yum-2.2.1-1.centos4.noarch.rpm