The AMCAS application is like many other things in life. If you have a logical reason for doing something (e.g., you have too many activities and want to compress two of them into one), and do it in a way that makes sense (e.g., combining activities into a logical catch-all category), you should be fine. In general, people don't get into trouble when they take measures like the one you are considering; they get into trouble when the are trying to obfuscate the truth, exaggerate or lie.