Halo headlights and turn signal question

Most older vehicles use a dual filament bulb, park circuit to one, turn circuit to the other. The halo is one so it must be one or the other. Both circuits attached to one would cause all sorts of back feed issues if not fuses blown or even wires melted if overload doesn't blow the fuse.
There is a way to do what you imagine, requires modifying the front fixtures for a 3 wire socket but...
since flashing headlights probably is illegal most everywhere, no need.