As wookiefriseur told you already, please read the sticky posts at the forum you are posting to before posting (
https://www.esoui.com/forums/showthread.php?t=9865), which tells you to please write about features and ideas directly inside the addon's comments. It helps the authors to track it more easily and it shows other users what was requested/reported so there are less double posts. Thank you
You can mark items in your inventory with "gear" or other custom defined marker icons with the addon FCOItemSaver.
You can then use an addon like Auto Category Revised to show those items in categories which you define yourself too.
FCOIS is not adding any context menu to ItemSetBrowser though, so this would be something that needs to be implemented into
ItemSetBrowser, BUT it only will work for itmes you got in your bag already, so this would not be anything that works properly with ItemSetBrowser!
In the end what you are searching for does not exist and would need to be added to ItemSetBrowser itsself.