As you might have guessed from PaulS's reply, there may be multiple copies of Print.h on your computer, but the Arduino IDE is only going to use one of them. Which one may even depend on which board you have selected from the Tools > Board menu. That Arduino Playground page was written long ago, when the situation was more simple (but far inferior). If you're modifying a different version of Print.h than the one the Arduino IDE is using, that's going to cause some confusion for you.
The easiest way to find the active hardware package location is as follows:
Select a board from the hardware package you want to find from the Tools > Board menu
File > Examples > SPI > BarometricPressureSensor (or any other SPI example sketch)
Sketch > Show Sketch Folder
Move up folder levels until you reach the one that contains boards.txt
From there, you will find Print.h under the cores subfolder (often cores/arduino).