Yes. A planetary gear may be changed under full power with no distress -
car autos have been doing this for years.


Not quite true. The gears are in constant mesh, but the one operating is
selected by a clutch band within the gearbox. Also, the torque converter
is a lossy liquid coupling which reduces the impact on the clutch bands
and the drive train when the ratio is changed. The only common
constantly variable drives( other than electric/electronic) are the twin
pulley ones as pioneered in cars by DAF IIRC and now used in some stand
drills. In cars I understand that these latter have an unequalled
reputation for unreliability. I believe the Japanese may now have
engineered a viable unit, but it's not on my acceptable list for a few
years yet.

Regards
Capitol