> db.contacts.update(

{"profile-id" : "test"}

, {$set: {"actual.0020000000000000000000": "val5"}})
> db.contacts.find(

{ "profile-id": "test"}

)
{ "_id" : ObjectId("4c2db755f6ec25d0c44c466a"), "actual" :

{ "key1" : "val1", "key2" : "val2", "001" : "val3", "002" : "val4", "0020000000000000000000" : "val5" }

, "profile-id" : "test" }

> db.contacts.update(

{"profile-id" : "test"}

, {$set: {"actual.0030000000000000000000": "val6"}})
> db.contacts.find(

{ "profile-id": "test"}

)
{ "_id" : ObjectId("4c2db755f6ec25d0c44c466a"), "actual" :

{ "key1" : "val1", "key2" : "val2", "001" : "val3", "002" : "val4", "0030000000000000000000" : "val6" }

, "profile-id" : "test" }
--------------

All working right, except last operation. As you see at last step key
"0020000000000000000000" was removed, and was replaced by
"0030000000000000000000".