I think if you ask the owners most will give you a bit of leeway most will obliged, unless booked up, you may have to check out and in again. I have done it a few times private albergue should be more accommodating.
On the topic of poncho vs rain jacket, I try and avoid religious arguments. I suspect preference won't be affected by route walked or time of year.
Since the Ingles is entirely in Galicia, I am confident in saying some rain gear will be needed.
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