I think im right. Its hard to tell, but I think its the personal upgrade type (not heavy weapon). It doesn't say replace just add and it becomes, presumably your unit leader turn into your spare normal trooper.
I assume that you could use the card on one unit leader with unit leader model and have the commander as well.
Its basically the addition action that snow troopers will get that makes this so good because they are harder to suppress. This makes it better than use a cheap second commander.
Edited by Winter79