How can I replace the 'Linen' that is prevalent in many Lion apps? There are many places where the "linen" texture is used in Lion, from the Login Window to various app backgrounds like Safari and so on.

Is it possible to replace this image with something else?  Let's say I have a nice hessian weave pattern from a lovely house I lived in that hasn't been decorated since 1979, or some sand, or a patchwork quilt depicting the transperambulation of pseudo cosmic anti matter?

Whatever I wish to change it to, a) can I change it, and b) will it change it for all instances where the linen appears, or does each application have it's own resources which would need ammending one by one with differing methods, and c) is there a particular size/fileformat/other feature that any replacement image must have, for example must it be a 200x200 PNG that tesselates etc.
The linen backdrop file is
/System/Library/Frameworks/AppKit.framework/Versions/C/Resources/NSTexturedFullScreenBackgroundColor.png

You can edit that file, or replace it with a file of the same name, but be certain that the replacement file has a resolution of 72 pixels per inch or you probably won't like the result.

ᔥ John Martellaro: OS X Lion: Change Login Screen’s Dirty Linen

Certain applications and situations draw their background from different sources. for example, the background file for Mission Control can be found at /System/Library/CoreServices/Dock.app/Contents/Resources/defaultdesktop.png

If you replace that file, you'll need to do a killall Dock command in the terminal before the change will take effect.

ᔥ OS X Daily: Change the Mission Control Background Wallpaper Image in Mac OS X Lion