I think this behavior is sensible. Additionally, you can disable rollback. However, cloud formation has needed and lacked a "dry run" option for a long time. It would be really nice to have that. However, the documentation does indicate what effect an update on any given resource will have.

I recommend against making sweeping changes to your infrastructure without thoroughness. Without saying this is what you're doing, I see a lot of developers who get involved with cloud treating changes whimsically. I'm not saying you should write perfect code. But thoroughness and a solid procedure (and backup plan) is a good place to start.