This incident is found towards the end of Chapter 8.
I would have to say that we are meant to find this amusing just based on the way that Orwell talks about the pigs and how they act. If he didn't want it to be funny, he would not have needed to put in all the details.
When I mention details, I am talking about things like:
- How Napoleon comes out wearing the hat and runs around the farmyard.
- How Squealer has "dull" eyes and how his tail is hanging limply.
- How Squealer announces that Napoleon is ill and about to die.
To me, a lot of these details could be left out if Orwell didn't want to make it funny. He could just have had the pigs get drunk and change the Commandment and it still would have showed that they are changing and becoming more like people. It would have had the same message without being funny.