Given or current sample size of 1, clearly we can.
It's the part where the teraforming produces a more habitable planet that we haven't gotten down yet.
But hey, this is only or first attempt!
In my view, given that we can do this, it is not unreasonble to assume that one day we will know enough to be able to tweak a planet's habitability in the opposite direction, or in other words, make an inhabitable planet habitable.
Aren't those the same thing? Shouldn't this be "make an uninhabitable planet habitable"?
The Earth's magnetic Van Allen belts deflect most of the sun's nasty radiation streaming at the planet. These belts are created by the molten iron core of the planet. Mars no longer has this magnetic shield, and the sun's radiation burned off the atmosphere. If we generate new atmosphere, it will just get burned off again unless we can generate some way of deflecting that radiation.
If we you can create an atmosphere it should last for a long enough period to be worth it, heck it might outlast humanity.
I have always thought that this would be a much more efficient way of living off Earth. Sci-fi wants us to believe that we can teraform planets. All they ever talk about are the atmosphere generators. However, they never address the reason the planet didn't have an atmosphere to begin with. To me, the research into generating artificial magnetic shields is the place to be. Generating those fields the size of a planet will be orders of magnitude more difficult than for smaller sized ships.