Nice job with Photoshop.
The stove is an add-on to a wood burning fireplace. I think the smoky rocks look fine and do not detract from the look. Its part of the charm. There are specially made cleaners for the discoloration.
Also - No way would you have good success in turning around the rocks. Filling in the vents may be easy enough but what if someone wanted to convert back to a traditional fireplace? They would loose the airflow that those vents supply (Albeit very limited in my experience). Same goes with filling in behind the stove.
If you really wanted new faces where you have dirty rocks, fill in the vents and fill in behind the stove...
I would either demolish the thing and start over or I would apply lath and a stone veneer. Either of those would involve removing the stove to do the work. Removing the stove should be relatively easy. It is very heavy though, could be 500lbs.
I'm not sure this qualifies as a DIY project regardless unless you have masonry experience.
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