There's more though. Next movie coming shortly!

: Curious as to the mechanism for them being friendlies, if a load zone is
: enough to switch them... maybe the devs just set the Flood globally to be
: allies until you go down rather than coding each one specifically?

That's exactly what I think is going on. After all, it wouldn't make much sense if the flip was just for the yeti Flood, since the game isn't even expecting you to be returning to trigger any.