Qualification 1: "In a situation where I have no clue what is going on, I may take certain things for granted in order to prevent paralysis, especially when I need to act quickly."
Qualification 2: "If I am in a situation where the difference between 'Probably p' and 'p' is irrelevant to the case at hand, I may use 'p' as a basis on which to act even though I only know that probably p."
I don't see why either of these are true in a sense that demands qualification of the rough first pass given above. With regard to qualification 1, let's suppose I'm in a situation where I have no clue what is going on. This isn't literally plausible, of course; in any situation in which my actions are rationally evaluable, I'll have some clue what's going on. So I suppose this must be understood as a kind of exaggeration. Perhaps, for instance, I suddenly find myself being charged at by a rhinoceros, and have no idea how I got there. It's clear, however, that if I just stand pat I will be very shortly gored to death. There's a button nearby with no label; I don't really have any clue what it is or what it does. But it may well be rational to press it, since that's the only real option I have and it's clear that if I do nothing, I will die. Maybe the button will open a trap door for rhino or for me—who knows? It's worth a try.
The thing is, all the premises that I'm using, if I so reason, are things I know. I know that there's a rhino; I know that I'll die if I do nothing; I know that there's a button; I know that maybe if I press the button I'll survive. So I don't see what pressure cases in which I have to act under extreme uncertainty put on the rough principle stated.
Similarly, if I'm in a situation where the difference between 'probably p' and 'p' is irrelevant to the case at hand, why think that I'm using 'p' as a basis to act? We've just stipulated that 'probably p' will do just as well—why not say I'm acting on that known proposition?
I don't really see what Hawthorne is up to in this footnote. (I suspect these issues may be developed in the later paper with Jason Stanley -- I read that a couple of years ago, but need to have another look.)