Can someone specify whether casting a spell in a non-mundane realm, assuming calm circumstances, automatically causes the roll to be a stress die? Does this change depending on which realm you are in?
I can't find a reference to it in the main book.

I know the number of botch dice are affected by the aura strength. But in the absence of a dangerous situation, does adding botch dice change a roll from simple to stress?

There are many ways for an SG to make a place from a Realm your maga is not attuned to stressful.
But if you find a calm situation there to cast a formulaic spell, ArM5 p.81 "... but in a calm situation there are no botch dice, even if the maga is in a strange aura (see page 183)" applies.

//... does adding botch dice change a roll from simple to stress?//
Usually extra botch dice because of strange Aura, special casting circumstances, even because of most flaws adding botch dice, are added only *if* the die which came up zero was a stress die to begin with.

Kind regards,

Berengar