This is advertised as a tool to make banks for Komplete Kontrol and Maschine but I have tested it with Massive X and it also works (as basically it is the same preset format for all)
https://www.doobox.co.uk/apps/mac/nksf_preset_banker.html
Now you can organise your user and third party banks like this (to add the thumbnail drop a folder into User/Shared/NI Resources/Image with the same name as your bank name and add a 72 dpi png sized 134x66 pixels named MST_artwork)
All credit to @Doobox for this (so send them likes)
https://community.native-instruments.com/discussion/comment/98290#Comment_98290