Hello Elite
Or even simpler use existing pediacons ,
like for example the one for the machine gun team might be apt for the Firebase.
I assume you know how to install units and know that if you duplicate pediacons you must copy the text EXACTLY.
The only drawback is your Civilopedia will have two units with the same pediacon and if you look at the forces garrisoned in a town/city you wont know exactly which are Firebases and which are mg teams , but as it is likely that your firebases will be fixed units outside cities it wont really matter too much
The game will work OK ...
Have a look at the Firaxis Napoleonic scenario and you will see what I mean , in that scenario several different infantry units "share" the same pediacons
I hope that this is helpful