To change the speed of the I2C compatible bus you use the I2CMODE register bit 0. If you are using version 1.2 of the Technical Reference Manual it may not be as clear. In one section it has the bit as a 0-read only. It is r/w and is called 400KHZ. The EEPROM configuration bit is stored in this bit. If you change the bit, the bus rate should also be changed.