Removing and replacing the keyboard on Toshiba Satellite A55 laptop wouldn’t be any different then replacing the keyboard on any other Toshiba laptop. Before you open the laptop case, remove the battery. The keyboard securing strip doesn’t have any securing screws and shouldn’t cause any problem when you remove it. The keyboard cable connector on the system board is cover by a metal plate and the plate has to be removed before you can get an access to the connector. Before you pull the keyboard cable from the connector you have to unlock it. To open the connector, move the connector lock toward the LCD screen. It is enough to move it 2-3mm to open the connector. Be careful with the keyboard connector on the system board. If you damage it, the entire system board has to be replaced.
By the way, if you want to remove the motherboard, you should take a look at the Toshiba Tecra A2 disassembly guide. Both laptops are very similar.