How to call directly a unit in a tag expression

[Aenur]

Hello, I am working on an army builder version for TOW. I have achieved to get some stuff working but I have long way yet.

Anyway, I now stuck in a detail I would like to ask for your help. I have created a list of magic armours the characters would be able to apply for (all gathered in an "option" and attached to each character by a "Linkset"). But of course, some of the character will not be able to select a magic armour, so for that my aim is to put inside this "Magic Armour List " option, in LIVE section, the name of the units I want to exclude from applying to magi armour. Here is where I get stuck. I would like to use the name of the unit directly to exclude:

!unitid.Assasin

But this doesn’t work, it says: "Tag 'unitid.Assasin ' not defined"

Anyone know how I can correctly write this expression?
I have been able to get it working creating a new tag group (an a tag) and giving this tag to the unit. But I would like to simplify the process.