Adafruit RGB LCD Shield but with a 20x4 LCD?? is it possible?

hi, im fairly new to Arduino'ing, im planning to buy the Adafruit RGB LCD Shield with the built in MCP23017 i/o Expander.

however i want to use a 20x4 LCD instead of the standard 16x2. will i have to do alot of modification to the library provided by Adafruit in order to work the 20x4 LCD?

heres what im looking to get:

heres a link to the library :

Thank you :)