I knew that there were timezone files on the system, and that they were some compiled version of source text files. I also knew that there was some link in /etc that told the system which timezone it was in. Searching Slackware's site for packages that deal with time got me a link to the site where glibc (Linux's C language library of functions) draws its timezone definitions from. That got me a pair of archives with raw source files and clear if already understood instructions on installing them.
Slowly the light dawned and I figured out that I just needed to invoke the timezone source file compiler (zic - already on the system) to compile a named file. Because there is an agreed upon standard for where to put compiled timezone files (/usr/share/zoneinfo), zic already knew where to put its output. On the older Slackware box there was a symbolic link in /etc (/etc/localtime) pointing to the right file down in /usr/share/zoneinfo/; that I re-made pointing to the updated file. On the newer box it looked like the installer copied the file out of /usr/share/zoneinfo/ and to /etc/localtime; easy enough to do manually.
Then I tested. The older box is my local NTP (Network Time Protocol) server, so I wasn't effing around with it. The newer box is 'just' a web server, so it got to be my guinea pig. I stopped Apache and Sendmail (as well as commenting out most of the jobs in cron) and advanced the time. I first told Solstice that it was 3/10 23:59 and let the time advance to 3/11 00:01 ... no change to the time. Oh, yeah, we do the shift at 2:00 AM! I advanced the time to 01:59 and waited. Zot! after sixty seconds the time jumped to 03:00 and the TZ changed from EDT to EST! Victory! I changed the time back and started all of the demons and cron jobs back up.
Now I just have to do this on a bunch more servers at home and at work:
Alas, the process for updating Windows 2000 machines looks far worse. Technically it's doing the same thing -- installing a new map of timezones into the OS -- but it's Microsoft so it involves arcane scripts and deep registry diving. I only have to deal with personal machines here, but that list numbers six at home plus another five if I add in my mom, my in-laws, brianrogers and elizabethbear. I suppose that poor Wingnut (my legacy Windows 95 laptop) is just hosed when it comes to the new timezone info.
Now, however, it is time for bed.
* "Computer System" in this case means any digital device with a clock and an automatic ST/DST adjusting function ... from digital clock thermostats to routers, PCs to multi-function fax/copiers. Mind you, the same government which brought us this act -- with virtually no consideration of the collateral effects -- is pushing to eliminate leap seconds from UTC (coordinated universal time) because dealing with them is too complicated. On hand clearly does not know what the other is doing.