Thanks for taking the time to open a feature request!

Is your feature request related to a problem? Please describe.
Its be good to add a flag for preventing an item to be attached with /hat on players hat (EssentialsX)

Describe the solution you'd like
add a flag to block it

Add the same setup with the /ah from CMI too please :)
Same issue

This feature has been added in the latest snapshot and has been tested as fully functional.
Simply specify the itemflag not-hat and the /hat command will be blocked for items with that specified itemflag.
In addition, a message will be sent indicating the action was prevented if the message is defined in the lang.yml file via commands.item.badCommand (will need to be manually added for older lang.yml files).

Link; https://ci.craftationgaming.com/job/ItemJoin/872/
Remember to remove your old ItemJoin.jar file

Let me know!~