[{"employees":[{"name":"Adam","_id":"5ea36b27d7ae560845afb88e","bananas":"allowed"},{"name":"Smith","_id":"5ea36b27d7ae560845afb88f","bananas":"not-allowed"},{"name":"John","_id":"5ea36b27d7ae560845afb88g","bananas":"not-allowed"},{"name":"Patrick","_id":"5ea36b27d7ae560845afb88h","bananas":"allowed"}]}]

db.collection.update({},[{"$set":{"employees":{"$map":{"input":"$employees","as":"e","in":{"$switch":{"branches":[{"case":{$eq:["$$e.name","Adam"]},"then":{"$mergeObjects":["$$e",{"bananas":"not-allowed"}]}},{"case":{$eq:["$$e.name","Smith"]},"then":{"$mergeObjects":["$$e",{"bananas":"allowed"}]}}],default:"$$e"}}}}}}])