I installed the Security Update 2018-002 on my Mac Pro 1,1 and was of course greeted with a boot loop. As I previously installed Security Update 2018-001, I had the kernel2017 lying around anyway, so I booted to Recovery, mv'ed kernel to kernel22018, cp'ed kernel2017 to kernel, et voilà, everything fine now.
Thanks for that report, I did the same thing and no problem so far.