I have the same dilema with regard to updating properties (color, linetype etc) of layers in an x-ref and have to go through the mind-numbing process of opening multiple files up and detaching then re-attaching the x-refs so their original properties are brought through. Visretain is ideal only if you dont have to make minor or singular tweaks to x-ref layer properties.
On that note, I have tried putting a "-layer" script together and running this through script-pro to apply changes to specific dwg files but to no avail as I have no idea how to overcome the layer naming of x-ref layers (which are prefixed with the x-ref filename). Any assistance would be appreciated.
PS: I also put together a script to remove and reload the x-ref - this works fine with script pro but on re-loading the x-ref, all clipped boundaries are lost for the particular x-ref. This is a further humbug as the clipped boundaries are not the same throughout the files having irregular shapes etc.