BTTG Excubitores

[Marco]

Hello guys,
maybe someone can help me with this.
In BTTG heraclian dinasty army, it's possible to upgrade the Bucellarii to Excubitore (if the emperor is taken and lead them). This upgrade costs 4pts and gives the Excubitores/Bucellarii a maces (hand weapon, so no special rules), heavy armour, shield and barded horses.
My question is: Do the Excubitores are allowed to take any other Bucellarii equipmet upgrade or they're tied to this almost basic equipment? Because if the latter is the caase i don't really get what kind of upgrade it is... (yes usually heavy armour and barding should cost 5pts and not 4pts, but in any case Bucellarii with kontos/bow are better than the Excubitores with their "reduced cost" equipment!)

Thank you in advance for any help.

Marco