Kathryn (and others), the bottom line appears to be that you should choose to treat the electrical panel (what would normally be treated as a Real Estate Improvement) as an Asset instead, due to the foreknowledge of the De Minimis deductibility. I'm okay with that and it seems to make logical sense. Because otherwise, TurboTax will assume you mean to treat this as part of the Real Estate proper.
Care needs to be exercised here, assuming that the De Minimis goes away. You don't want to do this type of action when this type of deductibility is no longer allowed or otherwise restricted.
