Repath an Xref
Have you ever opened a drawing and found that an Xref failed to load because it was moved or renamed on the network? You dutifully pick up the phone and ask the Project CAD Coordinator what's going on, and they tell you that the original background was not named according to standards, and that they've "fixed" the issue. So you detach the missing Xref that has the old name, then re-attach the correctly named background. Now you have to reset all the Xref Layer properties again: Freeze/Thaw state, Color, etc.
Try this instead: repath the existing Xref attachment (or overlay) to the new name. Open the Xref dialog, select the missing Xref, and Browse to its new name/location. This way you preserve all your previous modifications to the reference's layers.
AutoCAD 2006 and previous (or using the CLASSICXREF command in AutoCAD 2007):
Now your Xref name may not match the name of the file you browsed to, but you can easily fix that with the RENAME command, or by hitting F2 when the Xref is selected in the Xref dialog. This same methodology works for repathing/renaming Images too.