For discovery and autoregistration events, there are operations:

add / remove host
enable / disable host
add to / remove from host group
link to / unlink from template
set host inventory mode

https://www.zabbix.com/documentation/6.0/en/manual/config/notifications/action/operation
We need additional action like "set inventory field [choose field] value to", and with options to select: "static text" or "part of text from HostMetadata (by regex)"

This way, we can easily use Zabbix geomaps with private subnets. Also inventory can be filled with information directly send in autoregistration proces (no need for items on host = no vaste in history tables + free some machine resources needed for items).

Example, if we use the addresses 192.168.10.x for one location and 192.168.20.x for the other, we can set the corresponding coordinates in the inventory for both locations by discovery rules, using the option above (no external services used, no need for additional item and its scripts).
We can add an auto-registration rule based on HostMetadata, if HostMetadata contains specific text, then selected inventory fields are filled with some text from HostMetadata or static text.