Selecting "Update Apps" from the Control Panel triggers the suggestion that it's better to boot with the "base norestore" options and then run "tce-update" from the command line. I tried that, and got into a little trouble.
It seems like the option "base" caused the system to ignore my boot option "tce=..." and this made tce-update operate on whatever directory TC found during its automatic search. This turned out to be the wrong directory, because we are in this transitional period where it's fun to have two: one for version 2.x and another for TC 3.x. I stress that my trouble was little: TC makes it easy to recover from having all one's extensions overwritten. But still ...
Here are some suggestions born from this experience. Some may be more acceptable than others.
1. If a tce directory is specified using a boot option, make it stick no matter what. If the "base" boot option is also given, ignore the *contents* of the tce directory after duly noting its *location*.
2. Adapt the tce-update screen to announce the tce directory it will operate on *before* the user authorizes the start of the update process.
3. Add a "help" command that produces a list of TC-specific commands with terse descriptions, one per line. There must be one of them that lets me set the tce directory after booting, but I have forgotten it.
Thanks.