The expander.h is a library to use up to 32 devices in a SPI network (to save pines in the board), the expander enable the device connected to bus SPI with help to SS pin (53), i.e. the expander use 10 pines of the Arduino board (2 control and 8 direction) to drive 32 digital outputs with idle in high state.
Sounds to me like an overly complex alternative to a 4 simple serial output registers, that would use only 3 pins of the Arduino.
You do know that you can use any GPIO pin as an SS pin in SPI master mode, don't you?
Should I change the mode?
Yes.