Something like djmount would probably be better on a pi, given the low amount of resources. Might be worth looking into.

Yes, so replace step 5 with "in addon Replace file path of source (eg \\WDMYCLOUDMIRROR\) with desired file path on Pi (eg /home/pi/WDMyCloud/)"

The Addon can be set to use specific Path on exported Playlists if my memory doesn't fail me.

After much searching I have a work around to get Raspberry Pi to use MM library. Since my main listening is classical music the usual offerings are pretty useless at categorising music as I wish. VLC on the Raspberry could not cope with the size of the MM library when shared via uPNP/DLNA.
So the issue - I need (say) Clementine audio player on Pi to use MM library categorisation for a large (about 23,000 files/452 GB) mixed bag of different file formats, etc.
1 - I added the MM extension Export/Create Playlists for Child Nodes from http://solair.eunet.rs/~zvezdand/ExportM3UsForSubNodes.htm
2 - Select all albums (or selection thereof) in MM
3 - Use extension to create playlists for each (selected) album (all saved on the NAS)
4 - Mount the NAS which contains all the music files on the Pi - so that is now on the Pi as "/home/pi/WDMyCloud/Public/Shared Music"
5 - I used a neat (free) program called fnr to bulk replace the file path on the playlist files with the path as noted in step 4
6 - Then copied all the playlist files from NAS to Pi (/home/pi/Music)
7 - Then get Clementine audio player on Pi, Files option, to look at files in this folder - result is list of albums as per MM library

Not quick nor elegant but seems to be working.