So I succesfully rewrited all tooltips, except (I think) one :
The one displayed when you're in Quickslot Inventory and hover a potion in the Quickslot wheel.
It should be ItemTooltip, but seems, it's not this one.
If I /zgoo the potion, it's ZO_QuickSlotXButton (ex: ZO_QuickSlot9Button)
which have a sub key .activeTooltip = ItemTooltip
If I do a ItemTooltip:SetHidden(true), the tooltip is well hidden/displayed, but any of the functions used is setting the tooltip.
It shouldbe something like
ItemTooltip:SetSlotItem(slotIndex), but it doesn't seems to exists.