I think if you use a script call that looks like
BlizzCFG::Z_HUD_BACKGROUND = 'new_background'
it
should work (total guess). I've never messed with Z-HUD. Granted, that's a LOT of script calls if you want to modify each constant value listed under the configuration.
Just use 'BlizzCFG::' and then the constant value you want to access after it (such as Z_HP_FILE, or Z_SP_PER_TILE, or...you get the idea).