Answer
No — Custom Events in Cloud only support automated actions; interactive user prompts inside an event aren't supported anymore. For this kind of interactive, user-input-driven behavior, use a Workflow instead: Workflows support User Tasks when reacting to a Projection (API) call, and each User Task renders as a modal dialog in the client, giving a consistent way to prompt the user and branch on their input — something a plain Custom Event Action can no longer do on its own.