There is a public viewing area off the 4th floor concourse, but there are obstructions such as tree lines and monorail beams (and occasional monorails).
Those “balconies” that you’re seeing on both ends of the building are fire stair landings.
As such, I don’t know what alarms or sensors you might set off by opening those doors.
You certainly will not be allowed up to California Grill without reservations.
Plus, with a launch time of 8:51 (the window will only remain open for 10 minutes) you are butting right up against the absolute crush of people wanting to watch the fireworks at 9:30.
My suggestion would be to get friendly with someone who is staying on the Bay Lake side of the tower who will let you watch the launch.
If you are going to sneak into one of the fire stairs, the only one that will give you a view of the launch will be the northwest corner of the building. This gives an open view to the east north east and should allow you to see the launch once it climbs above the horizon. Because of the trajectory of a space station launch, the shuttle flies off to the north east.