I was going to ask about using an excerpt from a classical piece that was not in public domain in a song was on topic. In more detail, my question was going to be about how much I would have to change in order to steer clear from a copyright claim if that would be a problem. I don't know if that would fit in this community, so if it doesn't, could I be directed to where I could ask this question and have it be on topic?
Unfortunately, legal questions are off-topic on this site in general as stated in the FAQ. The reason is that it's typically out of the knowledge domain of a typical musician and even if one knows their local copyright laws, they may vary depending on where exactly you live.
The Law SE may cater to these types of questions and already seem to have a trove of music related copyright questions.