It can be undone since it leaves the files where they were and only makes copies.
1. make a backup copy of the itunes .xml and .itl file that are in the iTunes music folder so you can restore them if your new library isn't as you like it.
2. in advanced preferences tell iTunes the new drive is the location for the music folder.
3. consolidate
I don't know if it will end up as you wish but since the original files are where they were and you have the old iTunes libray files you can put it back as it was.
1. make a backup copy of the itunes .xml and .itl file that are in the iTunes music folder so you can restore them if your new library isn't as you like it.
2. in advanced preferences tell iTunes the new drive is the location for the music folder.
3. consolidate
I don't know if it will end up as you wish but since the original files are where they were and you have the old iTunes libray files you can put it back as it was.