Is a rebuildable atomiser more dangerous?
Not at all, as long as you know what you are doing. Rebuilding is not a stuntman's sport; it is a practice that requires discipline. If you use an electronic mod, the built-in protections will keep you safe in case of a short circuit. The danger does not come from the gear itself, but from a lack of knowledge regarding basic rules, such as using damaged batteries or inappropriate builds.
Safety relies on two pillars: Ohm's law and the condition of your batteries. Always check that your build has no short circuits on an ohmmeter or an electronic mod before firing. Also, ensure that your battery wraps are perfectly intact. By following these basic precautions, rebuilding is just as safe as vaping on a standard clearomizer.