I don't even think dfhack can do that. If you disable temperature it won't melt things.
Sorry to keep beating this dead horse but, could you use a material emission to shoot water into magma constantly turning it into obsidian I will attempt this later to see for my self but figured I'd ask
It does not sadly, I thought for some reason emissions left something on the ground....
Edit: disregard this post magma is hardcoded beyond what I want to do with it... Back to the drawing board
I wanted a magma swimming controllable unit
For the record for others trying this nothing that you can control(anything you can assign a labor to) will path into or over magma, magma at 1/7 breaks pathing and anything not caught in it will go the opposite direction or around it I think if it's possible, if there's no way out of the magma area the creature will not move any more(intelligent creature ai is blocked inside "closed" rooms) magma acts like barrier that at best can only be pathed over if also pathing away from) tiles touching magma are ignored)workwise
😭it can't even perform a job on a tile directly adjacent to the tile the creature is standing on, they effectively don't exist anymore
Which I'm assuming is happening cause they are stuck in an infinite loop of "get away from lava" and can't do anything else until "get away from lava" is achieved
Tested by leaving creature in closed room filled with magma and work orders for digging inside the magma filled room he stood there motionless even though 2 digging actions would have freed him from his prison