Stella wasn't a childhood friend of Noctis, though. They were to meet for the first time at that party, which is why I believe that Luna and other changes were Nomura's decision, not Tabata's
You know, that's a big possibility tbh. Maybe not the full name/looks change and all that, but in the E3 trailer we already saw a young girl (Stella, assumed back then) with the same dress Luna has in the newest trailer grabbing Noctis' hand. Nomura (afaik) never referred to the 2013 Stella as... well, Stella. He just said Stella (back then) wasn't his type of character and so he changed her (we all assumed it was only her looks).
So maybe. I always assumed, prior to Luna's reveal, that either that was a dream, a forgotten memory or something like that, o that they had changed their backgrounds for them to actually meet as children.