How can I make a new/copy old hidden resource and tie it to a unit?

i want to make a unit to be able to be build in only one settlement, doesn't matter who owns it. How can I make a new hidden resource/copy and existing one and place it under or near the settlement and tie it to the unit so that anybody who owns the settlement can build the unit?

If you cant find it over here look at the RTW modding forums, the info is easy enough to find over there ..;)


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