Out of interest, have you tried accessing the settings directly: $ xinput list
...
AlpsPS/2 ALPS GlidePoint id=16 [slave pointer (2)]
...
..so the touchpad is device id=16
$ xinput list-props 16
Device 'AlpsPS/2 ALPS GlidePoint':
Device Enabled (161): 1
Coordinate Transformation Matrix (163): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
libinput Tapping Enabled (314): 0
libinput Tapping Enabled Default (315): 0
libinput Tapping Drag Enabled (316): 1
libinput Tapping Drag Enabled Default (317): 1
libinput Tapping Drag Lock Enabled (318): 0
libinput Tapping Drag Lock Enabled Default (319): 0
libinput Tapping Button Mapping Enabled (320): 1, 0
libinput Tapping Button Mapping Default (321): 1, 0
libinput Natural Scrolling Enabled (296): 0
libinput Natural Scrolling Enabled Default (297): 0
libinput Disable While Typing Enabled (322): 1
libinput Disable While Typing Enabled Default (323): 1
libinput Scroll Methods Available (298): 1, 1, 0
libinput Scroll Method Enabled (299): 1, 0, 0
libinput Scroll Method Enabled Default (300): 1, 0, 0
libinput Middle Emulation Enabled (303): 1
libinput Middle Emulation Enabled Default (304): 1
libinput Accel Speed (305): 0.000000
libinput Accel Speed Default (306): 0.000000
libinput Left Handed Enabled (310): 0
libinput Left Handed Enabled Default (311): 0
libinput Send Events Modes Available (281): 1, 1
libinput Send Events Mode Enabled (282): 0, 0
libinput Send Events Mode Enabled Default (283): 0, 0
Device Node (284): "/dev/input/event7"
Device Product ID (285): 2, 8
libinput Drag Lock Buttons (312): <no items>
libinput Horizontal Scroll Enabled (313): 1
..so device enable is property id=161
$ xinput set-prop 16 161 0
..disables the touchpad (for example)