Both Grace and Smith tied for fourth at the U.S. Open, while Lowry tied for ninth.
They are eligible for unlimited sponsor exemptions for the remainder of the tour season as they attempt to earn 2015-16 PGA Tour cards through the non-member money list or non-member FedExCup points list.
Special temporary members are not eligible for the FedExCup playoffs, but can become regular PGA Tour members by winning an official event during the season and would then have their FedExCup points counted and be eligible for the playoffs.
The trio join Patrick Rodgers of the United States and Danny Willett of England, who also became special temporary members earlier this year.
(Reporting by Larry Fine in New York; Editing by Frank Pingue)