Now don't worry, I'm not going to bitch about anything you added Xaxl, I just wanted to clarify.
The method has also been used for terraforming or weaponized, creating a wormhole in a high-energy environment and shunting the heat to a planet. While this practice is commonly frowned upon in warfare, it has been proven capable of reducing a garden world to a boiling desert.
This is true, but entropy needs to be maintained. Heat always flows down-hill, from a hotter spot to a colder spot. In order to move heat from a cold region to a hotter region you need to fight entropy, which usually winds up costing you more waste heat that's generated, and entropy wins out in the end.
The point is that to create the boiling desert, your initial reaction chamber will need to be even hotter. Same applies for the ships, if the pile of rocks they are beaming to wind up hotter than the inside of their engine (which will happen if they stay locked onto that one spot too long) the heat sink shuts down and they need to recalibrate it to a new location.
I did have an alternative idea for how these things could be weaponized though… I got the idea from an Australian-American science fiction show (Farscape) in which they eventually discover wormhole weapons. The protagonist links the inside of a system's sun to the orbit of the planet they are at, which has a lot of enemy ships near it. The result is a kind of astronomical flamethrower that incinerates the enemy ships.
How I imagine it would work though is that the wormholes are much smaller, but they can still release a lot of energy. The first open end of the wormhole pops up in a sun (it could be nearby or far away, it won't make a difference), the second stage lies inside of your ship controlling the energy stream (and maybe siphoning some off to help power your systems). The stream then flows right into the 2nd wormhole leading to the third stage, your cold asteroid (or the poor hapless world that is being targeted).
It would require a respectable tech level to be able to have your ship handle the energy stream, but there are few things hotter than a sun… so you could probably target anything and maintain entropy. I imagine that to counter this a kind of "interdiction field" technology would start cropping up, preventing ships from FTLing into them without being invited, and preventing heat sink streams from siphoning star-matter under your feet without you noticing.