You can create your own articulation sets, or modify Art Conductor sets, and the articulations will show up in MetaGrid Pro, with the following taken into consideration:
When you create a custom articulation set and save it, it might take a few seconds before it is scanned by PlugSearch. If you would like to see the scanning progress, open the Articulations window in PlugSearch
Use unique names for custom articulation sets. If you use duplicate names, PlugSearch might send the wrong data to MetaGrid, as it can't differentiate between identical named sets
Save the custom sets in a folder in ~/Library/Audio/Audio Music Apps/Articulation Settings. Don't save them within the Art Conductor folder
Use only Note On and Poly Pressure switches in the articulation set
Custom articulation sets will be shown in MetaGrid Pro without categories
It's highly recommended to use Art Conductor for Logic, with over 10.000 of articulation sets it covers most if not all of your virtual instruments, and it will show the articulations categorised in MetaGrid Pro