2 ,for each class, are possible. For instance you'l sometimes get the chance to choose either a "Scouttrooper" or "Stormtrooper"...Scout being lighter armor but quicker.
As the mod grows im sure we'll add more troopers in these slots, even if the only differences are superficial.
"Government is the great fiction, through which everybody endeavours to live at the expense of everybody else."
Frédéric Bastiat