Depends what they mean by a cracked rear axle. The resr suspension itself can be removed and replaced in a weekend, though it's a pain of a job.
More likely the crack is in the chassis. Generally that will be due to rust, and the rear suspension would need to be removed for a decent welded repair. The inner chassis members can be repaired with the body on, but a decent repair to the outer mountings really needs the body to be listed off the chassis a little for access.
Later cars (or maybe only Spanish made cars) can crack on the inner rear chassis members just forward of the damper mounting. That can be repaired with the suspension still in place but the fuel tank removed. Still requires a welder though.