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Also, re: the last one on that list, I have the impression that the caster can choose any skill to be used in resisting the spell, so long as it makes sense. Is that true, or is it always athletics?
It's not the caster that gets the only say in what skill can be used to defend against the spell. The defender can rationalize suggestions, too, and the GM makes the final say.
For example, if the caster makes a rust spell, he could say he expects someone to defend against it with Athletics (to dodge the energy bolt).
The defender might be a great armorsmith, and suggest that since he made the armor, and the spell targets the armor, it should use his Craftsmanship (or whatever) skill to defend.
In this situation, the GM would probably nod and say, "yeah, makes sense."
And as for Rote attributes being locked in stone, remember, you still get the extra shifts from an exceptional attack roll added to your effect. I believe the book says you have to declare what they go towards in the creation of the rote (for example, to damage); though, I could be mistaken.