If possible it would be nice to be able to change the icons on the geo maps from the default.
Objects already have a "presentation image" property that is meant to control exactly this. It turns out it's currently ignored when the object is rendered on the geo map, so you always get the default icon there. I've opened an issue (https://github.com/netxms/netxms/issues/3399) to fix it — once done, your custom presentation image will be used on geo maps as well. Thanks for the report.