>     Note that if the oscillator's set to XT or LP, it can only be
>     reprogrammed to HS, and if it's set to HS, it can't be
>     reprogrammed at all... The only oscillator type that can be
>     reprogrammed to all of the others is RC.

Slight correction:

HS mode can be left as-is or programmed to LP.  XT mode can be left as-is
or programmed to LP.  LP mode cannot be reprogrammed.

Also note:

A device programmed for HS mode will work fine with a 4MHz crystal; it will
use more current than an XT-mode programmed device but may start more reli-
ably.  Most programmeers will refuse to program an HS-fused device if the
fuse settings in the hex file specify XT (change the hex file to HS).

While any device may be programmed for LP mode, only the LC devices are rated
for the lowest voltages that LP mode makes possible.  Some devices, such as
the 16C84, have fairly high minimum voltage specs even at 32KHz (except in
LC versions).