Assign double values to a property

Hi, All,
I am now developing a vassal module for a war game.
In this game I assign every piece with a “space occupation” property which
can be ground/air to define ground units and air units, but there is
a unique unit which can be both ground and air,
is that possible that I can assign two values, like ground and air to space occupation
property, so when I use global key command to search ground units or air units,
this unique unit can both be found and acted upon?
I have tried to add two marker trait like: space occupation=ground and space occupation=air
to this unit piece, but only one will work, the other one seems to be blocked since
they have the same property name.

I would probably attack this problem from the other direction. Instead of having your GKC search for just ground units, search for ground or ground/air. Then you can just make the Marker trait value for the unique unit “ground/air”.