Question for you Timex Eclair, can I use a star as the engine for my megaship? Pointing all the photons in direction?
http://www.popularmechanics.com/space/deep-space/a10885/the-...
Of course if this was happening we'd see some unusual proper motion from KIC 8462852. Which we're not. (Did someone check?)
Of course there would be all sorts of secondary effects, lowering the density in the core could slow down the rate of fusion, increased temp would increase it, but no garuntee that the effects would cancel. Also depending on how far out your mirror is the core might not ever notice the change. The outer layers could heat up and destroy your mirror before the increased temperature reaches the core.