4.5.2 heavily customized & hacked - any way to apply security patches w/o upgrading?

I have a website that is on 4.5.2 and heavily customized, so the mambo code is not the standard mambo code. Hackers have used Mambo security holes to take over the server, so we have had to unplug it from the network. The work to re-apply all the code changes to a 4.6.2 mambo is cost prohibitive. Is there an easier way to just apply the security patches and harden 4.5.2? Has anyone done this yet and have a set of patches that can be reused?