To return to how things were:
In JRiver select File > Library > Backup Library and make a backup of the current library.
Rename the drive back to original name.
In JRiver select File > Library > Restore Library
Your particles and everything else should be back to how it was
To leave the new drive name and fix entries in JRiver:
Select all files - easiest way is to use Audio > Files in the left tree and browse to old location
Select one of the files and then use Ctrl + A to select all of the files
Press F6 (shortcut for right click > Library Tools > Rename, Move, & Copy Files)
Select "Update datebase to point to new location . . . "
Make sure only "Find and Replace is checked"
Under "Find What:" enter the old drive name.
Under "Replace With:" enter the new drive name.
There is a preview window that shows exactly how the entries are being changed so you know you are entering the right thing.
I helped dlbeck do this a few weeks ago and all his Particles were retained with the drive letter change.
The Rename, Move, and & Copy Files
is an incredibly powerful and brilliant tool that has many uses. You can save all the settings as Presets and have multiple Presets. For example, one can rip all their Blu-rays to a single folder that isn't watched by Auto Import. After tagging and fixing cover art one can run a Movie, Concert, etc. Preset and have the files moved to your chosen directory. It will then be automatically imported into JRiver if those folder locations are part of Auto Import. Some use it for renaming all their vacation photos, reorganizing cd's by Artist/Album Name, and many other uses.