I'd have to say that Hermes doesn't seem like the kind of place to be so stringent with protocol as far as that goes (it's not a ridiculously long time, just a bit over) and that i'll bet they won't enforce it with you, what with you being a regular customer and all, etc. i think they are more likely to be strict with strangers.
D, no worries...I exchanged my RG Bearn for a Violet one and even though I told her it was more than 10 days she didn't seem concerned and swapped it out without any mention. I'm sure a scarf would be fine.
Hey I also brought in my Sequences...after a month...mine was in the black-and-whte colorway and just NOT me. None of my outfits suit so I brought it back in...my wonderful SA didn't even look at it, she said OK no problem with grace and smiles and that was it. Smooth exchange. The service at H is unbeatable. If you have a good relationship with your SA, just try, I'm sure they can accomodate your little request.