I think the word "spell" is ambiguous here. From more abstract to more concrete it can mean something that is on a character's spell list, or that's among a character's spells known, or that a character has prepared, or that a character has cast. Only when a spell is cast can it be interacted with.
Rkhet's interpretation seems to be that it is the abstract spell that is modified by the Permanent Emanation feat, and that for it to have tangible effect the spell must be cast. Thanee's interpretation is that the Permanent Emanation feat directly produces a concrete effect.
Say that I am an epic level cleric. Antilife shell is on my spell list, and there are no restrictions (like alignment subtypes) preventing me from casting it. In fact I have never cast it, but it is a spell I can cast, and so when I take the Permanent Emanation feat I can designate antilife shell as the spell modified by the feat.
Suppose I have done that. Do I now have an antilife shell radiating from me? Rkhet argues that no, I don't. The feat has modified the abstract spell for me (making it permanent and tenacious) but that doesn't do me any good unless I cast it. It is as if I researched a permanent form of antilife shell that I can dismiss and restart at will. My research modifies the spell on my list so that it has different properties, but it won't do me any good if I don't cast it. Rkhet's interpretation of the feat is that it modifies an emanation spell so that it has different properties; it is permanent, tenacious, and it can be dismissed or restarted at will. However, like the researched spell it doesn't do me any good until I cast it. I have to cast the spell first. Later on I can dismiss it and then cast it again. His question is whether I can then modify the AoE, at these subsequent castings, with Extraordinary Spell Aim.
Thanee's position is that the Permanent Emanation feat gives you a permanent emanation based on one of the spells you know. What emanation it is depends on the kinds of spells you can cast; you choose one spell you can cast that produces a permanent emanation when you choose the feat; the effect of the feat is that it comes into effect around you. You don't have to cast it; rather, taking the feat makes a instance of the spell come into being around you.
The key phrase is "This spell’s effect is permanent". One reading is that this applies to the abstract spell, which still has to be cast in order to have any effects. The other reading is that the feat brings into being a permanent spell effect. It is a concrete reading of the spell effect, not an abstract reading.
The problem is, what sense of spell does the previous sentence employ? "Designate any one of the character’s spells whose area is an emanation from the character. "
Read in a concrete way, it means that the spell has to be in effect when the feat is taken. There has to be an actual antilife shell currently emanating from the character in order to take the feat. Does anyone think that? Or is the abstract reading the correct one, that says that you look for a spell that the character can cast (even if he has never cast that spell) and see if it would make an emanation centered on that character?
There are equally valid rules of interpretation that can be applied here. One says that you should stick with an interpretation; if a spell is abstract in one sentence, it should be abstract in the second. I think that's Rkhet's rule. Another rule is that if something can be interpreted as concrete, that's what you should do. And since a concrete reading of the first sentence is impossible (it would require the choice of a feat to be taken at a particular moment in time, which isn't how feat choices are understood to take place), the first sentence has to be interpreted abstractly. But the second sentence can be interpreted concretely, so that is what you should do.
I wouldn't be inclined to grant Rkhet the combo he's asking for (with spell aim) so I'm inclined to agree with Thanee in this case. But Rkhet's case is certainly defensible.
