Bad cost basis -- fixable years after purchase?

[Sarah Albright]

Please, I have a problem that may be better understood by expert landlords. I used my purchase price on a multiunit residential property, minus land value, for the cost basis of my rental property. However the purchase price really didn’t do justice to the repairs and maintenance on the building. Now I realize I should have used an appraisal or some other valuation metric. For tax purposes, how can a cost basis be changed years after a purchase, even if it’s from the current year moving forward?

Example. A rapidly deteriorating building on cheap land for a very low sales price.

Commercial size apartment building, purchased for peanuts, kind of a “fire sale,” due to seller’s need to get out ASAP due to family issues.

Built in 1800s by a silk magnate, a Victorian mansion with ridiculous facets, dormers, outcroppings and silly business requiring exorbitant improvements, maintenance and repairs.

Land is nearly worthless, <10k value, in a very high crime area.

Insured for replacement cost at nearly 800k.

Maybe this calls for a fabrication...sale and repurchase for the sole purpose of adjusting the cost basis. I’d rather plead the IRS on a fair solution.

Thanks in advance for any ideas, information.