It's just that easy: Once your site is a designated historic property, the federal government will kick back 20 percent of the money you spend renovating it (pending application approval). Again, the applications for both designation and proposed renovations are available through the National Park Service.
However, there are a couple of catches. First and foremost, the property must generate income. You can't get this tax break for renovating your home -- that is, unless you have a home office or rent out space in your home, in which case you can apply for the 20 percent credit for renovations to this income-generating space. (This is a frequent tax break for bed-and-breakfasts.)
Second, your proposed renovations must be "consistent with the historic character of the property" [source: National Park Service]. The Secretary of the Interior provides a list of 10 guidelines that a renovation project must follow in order to be eligible for the 20 percent credit.