[{"_id":{"$oid":"111222333444555666777888"},"email":"xxx@mail.com","givenName":"xxx","familyName":"xxx","favoriteProducts":[{"soldTo":"33040404","skus":["W0541","W2402"]},{"soldTo":"1223","skus":["12334"]}]}]

db.collection.update({_id:{"$oid":"111222333444555666777888"}},[{$set:{favoriteProducts:{$cond:{if:{$in:["1223","$favoriteProducts.soldTo"]},then:{$map:{input:"$favoriteProducts",as:"f",in:{$cond:{if:{$eq:["1223","$$f.soldTo"]},then:{$mergeObjects:["$$f",{skus:{$concatArrays:[["12300"],"$$f.skus"]}}]},else:"$$f"}}}},else:{$concatArrays:["$favoriteProducts",[{skus:["12300"],soldTo:"1223"}]]}}}}}],{multi:true})