Please look inside the flare folder for the file  mods/fantasycore/items/items.txt

There you'll see lots of items defined, also there is

[item]
id=111
name=Lineage Signet Ring
quality=epic
item_type=ring
icon=200
soundfx=soundfx/inventory/inventory_gem.ogg
loot_animation=gem
price=1000
bonus=XP gain,25

The last line bonus= XP gain, 25 needs to change to 100 instead of 25, so you have an exp booster ring.

Feel free to also change the prize, name or other attributes.