The function that fires the site wide system feed share action is
jrOneAll_db_create_item_listener() found in:
/modules/jrOneAll/include.php
Currently it:
* checks the user is logged in,
* gets the linked network for the System Feed (if it exists)
* retrieves the owner of the created items info
* creates a 'share_action' queue.
There is no code in place to limit it to specific quotas.
There is an event that happens when the queue entry is created though:
'create_queue_entry', you could use the events and listeners system:
Docs: "Events and Listeners"
https://www.jamroom.net/the-jamroom-network/documentation/jamroom-developers-guide/1011/events-and-listeners
To listen for that event, then fire your own function to drop any items that were in a quota you didn't want being added.
