That could be done without targeting individual companies so yes. Same as it is legal to give incentives to buy green cas by subsidizing light or electric cars taxing gas or heavy cars.

The kind of targeted breaks I'm thinking of is e.g. this: http://app.leg.wa.gov/billsummary?BillNumber=2089&Year=2013#...

That's just basically Boeing saying "Give us a tax break of N billion or we move from Washington". Legislators afraid to lose their jobs approve. The state keeps the jobs, the legislators keep their jobs. Everyone is happy? Well, except the people in the state that lost a ton of tax revenue.

To be clear: this isn't a tax cut for "the Washington aerospace industry". There aren't going to be any competitors creating buildings for the manufacturing of plane fuselages in Washington state - it's a tax cut directed directly towards Boeing alone. You wouldn't have to be a star lawyer to prove that point.

The argument that "but they create jobs in the state so even with the tax break, Washington state benefits from having them there" doesn't float either. That's how blackmail works. I need my knee caps so even after paying the mobster $10000 for keeping them I come out ahead!

If states weren't able to offer company targeted tax breaks like that, then Boeing couldn't have blackmailed Washington legislators like that. Which would benefit everyone involved (Except of course - Boeing).