Can you post a link to some pictures? There are all kinds of fasteners, and
knowing which one they are exactly would help. Are they nail ins? Lead
shielded lags? Wedge anchors? It helps to know. Not a lot of concrete
fasteners can be removed once they're in. They're designed that way.

I was a steel erection contractor for nine years. I serviced 275 different
apartment properties. I ran into many many different situations. Some were
easiest to just put a different plate on there that would just cover up the
old stuff and look like new. Other times, chisel it down, burn or cut off
the stub, and use PourStone to get an acceptable looking plug.

You can only make so much ice cream out of so much horse manure. Sometimes,
you can't get there from here, and have to find a plausible alternative.
Very seldom do you get the old fastener out and get to put a new one in the
old hole.

Keep us posted, and link to some pics if possible. I use Flickr. It's easy
and free, and one picture is worth ten thousand words.

Steve