The mod is made by Fizzer, so perhaps the easiest way would be to contact him and ask him to update his mod?
Otherwise, maybe create a pull request on the mod's github page
https://github.com/FizzerWL/ExampleMods/blob/master/GiftArmies2Mod and present some code there?
Fizzer will probably accept the pr without asking too much fuss.
Should you decide to do this yourself, what you are looking for is described on
https://www.warzone.com/wiki/Mod_API_Reference:GameOrderEvent, with the
visibleToOpt parameter of the function.
For light fog, you probably have to combine this with GameOrderCustom to create seperate messages for the players that are allowed to know the numbers, and seperate messages for those that should only see that something was gifted.
I recommend you join the mod makers discord (
https://discord.gg/5gs9JhyT), since all active mod makers are on there. Discord is also better suited for talking about code than WZ forums.