If you had the technology to even seriously think about harnessing the power of a star for propulsive purposes, moving a planet to a new orbit would be trivially easy.
More to the point: terraforming -- the intentional change of a planet's atmosphere to alter its average global climate and gas mixture -- doesn't require any new technology we don't already have (just massive amounts OF it applied for an incredibly long period of time). We do not even have a serious concept of what kind of technology would be needed to directly harness the power of a star in sufficient quantity to MOVE that entire star across interstellar distances; we do not now even know HOW to move things across interstellar distances, and transporting a star across that gulf is a whole other ballpark.
How would Robert Zubrin change a lightbulb? He'd build a tiny black hole in your living room and then harness its hawking radiation to emit a limitless source of visible light. That's got to be easier than walking down the street and buying a new one.
