Can a war of self defence turn into a war of aggression?

I'm sure that it could, but this clearly hasn't happened yet. We still see lots of high-quality videos of buildings being bombed by Israel. That is possible only because Israel warns civilians away from such structures. In a war of aggression, such warnings would not happen, and such videos would not exist.

I would say yes. The question is what definitively makes it that. So far, all I see is subjective judgment. Even in official reports, when you go deep enough in official reports from various organizations, it feels subjective.