At the password screen, select the Japanese character on the 3rd Row of the 3rd Column and enter it 12 times. Now hit "End" and you'll get an error message. Just hit enter again to start the game with 10 planets occupied.
9 Occupied Planets
At the password screen, select the Japanese character on the 1st Row of the 4th Column. Then 3rd Row of the 3rd Column. Then 4th Row of the 2nd Column. Then 4th Row of the 4th Column. Repeat the same set of Japanese characters 2 more times. Now hit "End" and you'll get an error message. Just hit enter again to start the game with 9 different planets occupied.