(Adds shares) Dec 15 (Reuters) - WPP, the world’s biggest advertising firm, said on Tuesday it would restate its financial statements from 2017 to 2019 but its headline operating profit, debt and cash flow were not affected. The British company said its presentation of cash and overdrafts as part of notional cash pooling arrangements did not meet accounting norms, while net investment hedging was inappropriately applied against some foreign exchange exposures. WPP said in a statement that the adjustments will not impact on any of its headline measures of operating profit, net debt, net assets, net current liabilities or statement of cash flows. To mitigate its impact on future periods, the owner of the Ogilvy, Grey and GroupM agencies said it would change the cash management strategy during 2021 so that certain cash and overdrafts will be settled or offset. WPP shares were flat in early trading. (Reporting by Tanishaa Nadkar in Bengaluru; Kate Holton in London; Editing by Arun Koyyur and Alexander Smith)