Is changing the front sway bar on a 2000 Cadillac Deville hard

Not particularly, but it is very uncommon to need a new one. They rarely break. It IS very common to need new outer links. They are real easy to install new ones but getting the old ones off can be a chore if all you have is hand tools. If the bolt is already broken, the parts can be slid off but you'll have to fight a little if the sleeve is rusted to the bolt.

When you install the new parts, tighten the nut just enough until the rubber bushings expand to the same diameter as the metal washers. That leaves them flexible enough to move around freely.