Xara are mostly already at a solution to this.

It uses .xar files with a specific filename format to apply Colour Schemes.
I believe that you can save a XAR file with Theme Colors 1 to 5, possibly Text & Website backdrop as well. Then rename the file to anything_themecolorschemenn.xar.
If this file is dropped on top of your design, the Theme Colors are updated to the new colour scheme; the actual design page contents are ignored.

I have not checked it other than renaming Gary's Palette file to gp_themecolorscheme88 and it seems to add the Named Colours correctly to the Colour gallery and the Colour Bar.

I am sure this is what jclements (OP) was implying but it might have been overlooked.

Acorn