What data format for object (like JSON) supports in place update?

Hi, I want to ask if anybody knows the data format for object serialization that supports in place update (updating a field of object does not cause the rest of object to be copied to another memory location to fit new size of this object)

Yes, but they are not efficient: When updating one small field, like string, which is larger than the original one, the whole document must be resized too, to have enough space for the updated field. This is inconvenient.