Yes they are interchangeable. However the correct grammatical structure for this text should be "I know you have a party to attend, but that can't be an excuse or reason to skip a class." In the English language the word /but/ is a conjunction and therefore shouldn't be used to begin a new sentence. Book a class and let's learn more about conjunctions and sentence structures😊☺

There is a difference in meaning between "excuse" and "reason." An "excuse" is a reason. But it implies that the reason is not true, logical or acceptable. It has a negative connotation. The word "reason" alone is neutral and simply means "an explanation." I would suggest the following as better options: "That isn't an excuse to skip class." "That's not a good excuse for skipping class." "That's not a good reason to skip class." Notice the use of "not a good reason" instead of only "not a reason." Going to a party is "a reason"; it's just not a "good reason."

The reason I cannot answer your question is that I never learned English grammar at school. But this is no excuse, because I could have studied it after leaving school. In spoken English, people use them interchangeably. Apparently, in grammar, there is a difference. As Erik suggested. But, give me one good reason why I should learn grammar :-) Sometimes there is neither rhyme nor reason for doing something.

Yes, you can use them interchangeably in this context. I know you have a party to go to, but that can't be an excuse to skip a class.