I found that after adding customizations to a barrel, I could not "reset" it to default state. It also meant I could no longer stack those barrels in my inventory, and other issues related to bulk updating/stacking/etc. From an aesthetics standpoint, I also could not get them to "match" other barrels anymore, there was also something a little off...

you can reset it using vanilla cauldron, the same way you would vanilla leather armor