Another way would be to edit the collections config files directly. We don't normally recommend this, as it's easy to corrupt the data with a bad edit, but if you're replacing X:\ with Y:\ then it's hard to go wrong, and a quick way to batch edit the paths.
The files can be found in /dopusdata/Collections and are in XML format (assuming the option to compress collections is turned off; it's off by default).
Be sure to fully exiting Opus (via File / Exit Directory Opus) before editing any of them, or your changes could get overwritten by cached data that was already in memory.