It seems to me anyone with the technology to modulate the oscillations of a variable star (without destroying it altogether) would be able to transmit omnidirectional signals in a variety of ways. The ability to interfere with thermonuclear processes deep in stellar interiors and produce a controlles and recognizeable artifact is a Type II or III capability. It makes the construction of Dyson Spheres look like child's play.

Like all these other hare-brained schemes to send beacons or messages across interstellar distances, the major problem is not sending the message, but doing it for a long enough time that someone will likely be looking in your direction when you do. Then you have to postulate that the transmitting civilization doesn't care whether it takes thousands or even millions of years for the message to be seen (Cepheids can be detected over extra galactic distances even with early 20th century technolgy (that's how Hubble proved M31 was another galaxy). And of course, the active civilization will then have to wait thousands (or millions) of years to get an answer, IF the message recipients chose to reply. I suspect that civilizations who have the capability to do this will have better things to do with their time and resources.