That's not quite how it works. Publicly-traded companies don't reduce their net income using a tax cut, because their entire industry is getting the tax cut. The company's market price is tied to how their NI compares to the rest of their respective industry NI.

Stock repurchases are filed on the balance sheet, post taxes, which is why companies take the increase in net income but then use the extra cash to buy back stock. The former keeps the company competitive and the latter increases the stock price.