Cat Exhaust Bolt Removal

So my bolts that go to my header on my focus svt are completely rusted. I attempted to remove the nuts, but they are too rusted to get off, they end up just rounding. This was originally being done to replace the oil pan, since it is leaking.

My question is, are these bolts welded/pressed in to the cat, or are they bolts that can easily be hammered out? Everyone just keeps saying cut the bolts off, but getting them out will be the hard part lol.