Name of this shelf support screw with plastic head

Yes. They can easily take the weight when anchored to studs. I use it for my computer desk. It works great and gives you a very inexpensive, height adjustable, and narrow depth desk. I have two shelves. One is 24" deep and is a keyboard/work surface. The other is just 12" deep and holds my LCD monitor.

I opted to place just two rails ~32" apart (skipping one stud) so that my knees don't bang the brackets. This causes the desktop to bow very slightly under the weight of my hands. I suppose this could be fixed by using a more rigid surface vs. the default melamine shelving.

My PC is on the floor but these shelves could easily hold the weight.

Yes - It does sound feasible. A few things I would consider for cutting off the lag bolt heads.

1. Install the bolts first into the wall studs so you can utilize the heads for screwing in the bolts. Do not make the common mistake of forgetting to pre-drill a proper sized pilot hole for the lag bolt threads into the stud.

2. Use a reciprocating type saw (i.e. Sawzall) with a high quality metal cutting blade to cut the bolt heads off.

3. Dress up the cut bolt stubs to eliminate the sharp edges by using a Dremel type tool with a small grinder stone.

4. Only now mark the shelf pieces for the proper hole locations and drill your holes into the shelves.

Additional considerations -- --

1. A 4 x 24 inch shelf cannot get too much stuff on it. You may consider using a smaller size than 1/2 inch bolt and achieve a suitable result. A 1/2 inch lag into the edge of a stud has to be very carefully centered on the stud.

2. Consider safety factors regarding shelves that can simply pull off the wall mounted studs. You may want to consider the possibility of some type of set screw in from the top or bottom side of the shelf that would help clamp the shelf to the bolt studs. (You could of course glue the shelves to the bolt studs with construction adhesive but then the installation would be virtually permanent).