By forcing Goldman Sachs Group to admit a “mistake,” US regulators may be signaling a more confrontational approach to future settlements that could expose Wall Street to more investor lawsuits. In its $550m accord with Goldman Sachs, the Securities and Exchange Commission deviated from its usual practice of imposing a fine while letting a firm remain silent on whether it engaged in misconduct. Firms required to admit oversights may find it difficult to argue in private litigation that they conceded no wrongdoing and settled purely to end regulatory scrutiny, said Salvatore Graziano, a lawyer who specializes in class-action securities fraud suits.