I tried that, and darn near stabbed my hand in the process. I know it's theoretically possible, but I wouldn't call it easy.
Where I'm from, nuk pacis come in many different shapes. I'm guessing you're looking to modify the classic one? There's tutorials online for that. Here, we also have the freestyle range, which has buttons that do come off but are easily broken when you pry them off, and the genius range, which can't be taken apart at all.
The only pacis I found truly easy to modify were MAM ones, but I'm guessing you already know about that. They don't use glue, so you don't have to worry so much about breaking anything, and they have a convenient edge at the button to pry them open. Though I must say, the MAM perfect and MAM air have a different button shape which makes it harder to get open than the MAM classic.