Starting with Minecraft 1.16.5, install Fabric loader and Fabric API.
Install mobdisguises-1.0.0-fabric and disguiselib-1.0.2-fabric.
Create a new world with cheats enabled.
/summon cow (summons an undisguised cow)
/summon minecraft:cow ~ ~ ~ {CustomName: '""', DisguiseLib: {DisguiseType: "minecraft:player", DisguiseAlive: 1b}, UUID: [I;-2098678989,-1503901171,-1600499207,-1228930832]} (summons a cow disguised as a player, also works with non-player disguises)
/give @p bucket 16
Milk the disguised cow. You will get a milk bucket, but no entity.cow.milk sound will play.
Milk the undisguised cow. You will get a milk bucket and the entity.cow.milk sound will play as usual.
To reproduce:
mobdisguises-1.0.0-fabric
anddisguiselib-1.0.2-fabric
./summon cow
(summons an undisguised cow)/summon minecraft:cow ~ ~ ~ {CustomName: '""', DisguiseLib: {DisguiseType: "minecraft:player", DisguiseAlive: 1b}, UUID: [I;-2098678989,-1503901171,-1600499207,-1228930832]}
(summons a cow disguised as a player, also works with non-player disguises)/give @p bucket 16
entity.cow.milk
sound will play.entity.cow.milk
sound will play as usual.