When i give myself an villager egg with custom career :
summon item ~ ~ ~ {Item:{id:villager_spawn_egg,Count:1,tag:{display:{Lore:["Farmer"]},EntityTag:{id:"minecraft:villager",Profession:0,Career:1,CareerLevel:1}}}}
or with
summon item ~ ~ ~ {Item:{id:villager_spawn_egg,Count:1,tag:{EntityTag:{id:"minecraft:villager",Profession:0,Career:1,CareerLevel:1}}}}
And when i use the egg, I got a Farmer. That's what i want, but this farmer got others career trades.
Confirmed for 1.13-pre7