Since Aranea's trolltag was the same as Vriska's, aG, when she trolled with Terezi, can we say that the trolltag of the Beforan trolls would still be aA, aT, tA, cG, aC, gA, gC, cT, tC, cA and cC?

Yes, it’s likely all of their Acronyms are the same, but with different Troll Tags potentially.