Here's an example of replacing just the keyboard on a MacBook Pro 15" Unibody (Mid 2010). It should be relatively similar for years 2009 and 2010.
[http://www.insidemylaptop.com/disassemble-macbook-pro-15-mid-2010-replace-keyboard/|Replacing keyboard on MacBook Pro 15" Mid 2010]
You'll have to disassemble the notebook as it shown in one of the guides on iFixit and access the keyboard. After that you carefully remove the backlight and unscrew the keyboard.
[image|219119|align=left]
I'm typing on a MacBook Pro with replaced keyboard. :)