Custom Villager Trades

So I  know i can change trade item, and qty required.
and i typically have used the below to update trade item.
So this is for mending level 2 book
/data modify entity @e[type=minecraft:villager, sort=nearest, limit=1] Offers.Recipes[1].sell set value {id: "enchanted_book", Count: 1, components: {stored_enchantments:{levels:{mending:2}}}}
And this works fine.
but how do i change a villager trade to a custom enchantment book after villager has spawned.
so lets say i have datapack:life_steal.
I've tried replacing 'mending' with
life_steal
"datapack:life_steal"
"datapack:lifesteal" 
and it doesn't work