You will need a modded version of the GalaxyScenarioDef that includes entries for the new assets...add the assets just like the other capital ships are added (update the "counts" as well) and then you should be able to select thing via galaxy forge (assuming it is using your newly modded GalaxyScenarioDef)...

I don't have the files in front of me so I can't give a more detailed explanation at the moment....

How would I go about making a moded GalaxScenarioDef file then? Because the current file for Rebellion doesnt have them included so I guess that it falls to me, or any other Sins player/modder, to make one for themselves.

Ahhh what? I totally thought planets could have boners!

Cursed typos. Meant *bonuses*

Ah I figured it out. But thank you Seleuceia for steering me in the right path.

Sorry, I should've first stated I was working on the GSD for a different mod. For those wondering what they need to do, you have to go into the original GalaxScenarioDef file in the actual "sins of solar empire rebellion", find/scroll down till you get to the part that says:

planetItemType
    designName "Psi:CapitalShip:BattleShip2"
    entityDefName "CAPITALSHIP_PSIBATTLESHIP2"

(thats for the new Vasari Cap ship), open the GSD file of the mod you're working on, find/scroll down to the section that says: "planetItemTypeCount", add three to whatever number is there (3 for the 3 new capital ships), and then insert in the sections (like the one I showed before) in line with the other planetItemType passages.

You are wrong my friend.

TECH = TEC
PSI = Advent
Phase = Vasari