Sounds like some monkey with an air wrench tightened the lug nuts WAAAAYYYY too tight!
Yes, the lug bolts can be replaced. You can just hammer them inward. There's a press fit spline that holds them in. When you get the new lug bolts, just use a wrench on a lug nut to pull them into their press-fit holes.
The rotor isn't welded on. Probably just rusty. Spray some penetrating oil on it; like PB Blaster or Liquid Wrench. There should be a couple of tapped holes that you can thread a screw into - use them to push the rotor off. I don't recall what thread size they are. Metric, no doubt.
You *do* have the brake caliper removed, right? If not, that needs to come off before the rotor will.
Yes, the lug bolts can be replaced. You can just hammer them inward. There's a press fit spline that holds them in. When you get the new lug bolts, just use a wrench on a lug nut to pull them into their press-fit holes.
The rotor isn't welded on. Probably just rusty. Spray some penetrating oil on it; like PB Blaster or Liquid Wrench. There should be a couple of tapped holes that you can thread a screw into - use them to push the rotor off. I don't recall what thread size they are. Metric, no doubt.
You *do* have the brake caliper removed, right? If not, that needs to come off before the rotor will.