This is hacking and might not work in future releases of the AmigaOS
Maybe

However, using a task's userdata field is not hacking, using signals is not hacking and passing memory blocks between tasks is not hacking (unless the Amiga API gets incompatible with itself and makes demands such as "owner must free memory"). SIGF_SINGLE signaling was apparently documented on a developer CD. I suppose I picked up its use for task handshaking via Olaf Barthel's Term source code. It had a funny comment: "Task termination and handshake signal. Note: don't try this at home kids, we are all trained professionals here!".