NEW YORK, Aug 4 (Reuters) - ValueAct Capital is reordering its management team and promoting long-time partner Robert Hale to co-chief executive alongside Mason Morfit as the investment firm focuses more heavily on Japan and wants to simplify its own organization.

At the same time, ValueAct told investors in a letter seen by Reuters that three partners, including the firm's president Brandon Boze, are leaving. Boze will retire from the firm in 2024 and partners Dylan Haggart and Sarah Coyne will leave.

After posting a 20% gain in the first half of the year and beating the S&P 500 index, ValueAct said investors are facing "a new market regime." The firm said it made changes internally to "miss fewer opportunities, and reduce our mistakes."

ValueAct, which has pushed companies ranging from Microsoft to Salesforce to change, wrote that it applied the "blank sheet" approach it urges target companies to adopt for itself.

The moves mark the biggest changes at San Francisco-based ValueAct since 2020 when Morfit took over as CEO after the firm's founder, Jeff Ubben, stepped aside and eventually left.

Morfit, 45, who arrived as an analyst at ValueAct two decades ago, picked Hale, 38, as his co-CEO after a decade of working closely together with Morfit running the global Flagship Fund and Hale taking primary control of ValueAct's new Japan Fund, launched earlier in 2023.

Hale has served on two Japanese companies' boards: chip maker JSR, which last month agreed to go private, and optical and digital precision technology company Olympus. ValueAct also pushed to replace four Seven & i Holdings directors with its own candidates this year, a campaign rejected by shareholders.

"Rob has built what we believe is the premiere engagement investing franchise in Japan," the letter said.

ValueAct said it has been working on these changes for months. "Our goals are to reduce volatility and apply insights more quickly."

Haggart, who will remain a director at Fiserv and Seagate, is leaving as he wants to manage his own investment portfolio, the letter said. ValueAct said Coyne identified long-term super cycles as the market reached to short term datapoints.

ValueAct made headlines earlier this year when Morfit was appointed to the board at cloud computing company Salesforce which was facing pressure from four activists, including Starboard Value, Elliott Investment Management and Ubben's Inclusive Capital. Performance has improved and the stock price has climbed 60% since January.

ValueAct's investments in Salesforce, Spotify, the New York Times and Insight, were built during last year's stock market collapse and have contributed to this year's strong returns.

(Reporting by Svea Herbst-Bayliss Editing by Nick Zieminski)