The US extended DST by 4 weeks in 2007. We managed that well-enough. We can manage a similarly-sweeping change again.

(Sorry about your nightmare. It was easy on the systems I took care of at that time.)

Obviously I would have forgotten most of this given the change was 20 years ago but IIRC DST config on Solaris at the time was statically coded. You could modify the timezone config as a hacky fix on Solaris 8 but the permanent fix involved recompiling zic.