Create the file /etc/udev/rules.d/98-ms-ergo.rules with the following contents:
ACTION=="remove", GOTO="keyboard_end"
KERNEL!="event*", GOTO="keyboard_end"
ENV{ID_INPUT_KEY}=="", GOTO="keyboard_end"
SUBSYSTEMS!="usb", GOTO="keyboard_end"
SUBSYSTEMS=="usb", IMPORT{builtin}="usb_id"
ENV{ID_VENDOR}=="Microsoft", ENV{ID_MODEL_ID}=="00db", RUN+="keymap $name 0xc022d pageup 0xc022e pagedown"
GOTO="keyboard_end"
This will map the zoom key to page-up/page-down without changing the installed files in /lib/udev.
Once added, you just need to unplug and replug your keyboard for it to start working.