Yes, you'll have to rebuild it. I can't remember right now what i did exactly back then cause i was experimenting a lot. But as far as i can tell i think i updated using kalyway10.5.3comboupdate, i used to log into my osx installation on spare usb hh and install this update on my working osx partition. Then install kexts, applied patching, etc.

Right now you'll have more work to do with rebuilding the package. It all depends on what you are planning to do with it, keep it for later reinstalls, etc. I think you have somewhere to d'l pre-patched 10.5.4 update for AMD, i think i downloaded it and have it somewhere. Also you can directly install 10.5.4ComboUpdate you have right now. There is a howto from netkas and also some of them on insanely mac forum. I'd suggest you should back up all your working kexts, never forget to back up, and it'll be good to use spare partition, external usb drives for such things.
http://forum.insanelymac.com/index.php?showtopic=107340
Its all pretty well explained, 10.5.2 -> 10.5.3, but it will work for the latest update too. You'll have to install the kernel later, make list for batch patching, etc.. if you decide to go this way, boot into another leo installation and install it onto partition you wish from there; not to install it to installation you're logged on.