With Poser 12, you even have an easier way: just drag an image file from your file explorer directly in Poser's Material Room, in a place where there's nothing.

And if you do the same on an existing image node, Poser will ask what to do, letting you the opportunity to search and replace all occurences of the same picture with the new, be it on the figure, the scene. The choice is up to you ?

Example:

𝒫𝒽𝓎𝓁

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