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Usually when someone needs this done, it's for printing on fabric, such as screenprinting. But for 256 colors, it's probably not that.
If it's a worthy enough use - meaning something other people will likely need in the future as well - it increases the chances that a developer or advanced user might be motivated to write a script or maybe even new extension.
Plus, we're always excited to learn how people are using Inkscape! This sounds very interesting!