A picture would help, but take another look
Welcome to the forum.
Unless you are the victim of a clueless previous owner, the bolt is not welded to the shock.
The lower shock mount is, however, a stud mounted to a flange welded to the axle arm. At first blush, it looks like the entire axle needs to be removed to get the shock off.
Inland Andy recommends bending the flange just enough to remove the shock. I agree with his suggestion, and did just that when I replaced my shocks. It worked like a charm.