Could we see a pic? Is it the intake vent? I'm sure there is way to do it. But why call attention to it. If in a place you could add furn in front or over it like a table, would work. But I think just painting the same as wall would be the best. Not sure what you mean about adding a quote? No writing on walls please. Those days are gone.

Thanks for your reply - the catch currently is that their house is in NZ and I'm over in the UK with the intention of doing this all without them knowing as a Christmas present. How far I get before my cover is blown is anybody's guess. I'm currently waiting on a picture under the ruse of 'asking about gas central heating for a friend' and will be sure to post.
It is the intake vent I believe and is quite sizable (again waiting on exact dimensions but approx 18" x 25").
In a house where everything is wood or William Morris wallpaper it's a large white plastic grille so it's calling too much attention to itself as it is. In an odd way, the more considered it is, the more it will sit in with the rest of the house. The hallway is not wide enough to put even a slim table in front of unfortunately.
In regards to adding a quote - while not the best example, see the attached image for examples of how Arts & Crafts style furniture would sometimes have a little phrase integrated into the design. Definitely not essential for this project but might be a nice little touch. I'll try and come up with a concept shortly to post and put up the images as soon as they arrive. I'm fairly confident I can have a decent crack at the aesthetics but need to be careful with things like keeping the right amount of airflow etc.

(The image is from http://www.millineryworks.co.uk/pages/Furnitureexhibitions_Shapland&Petter2.htm)