Assigning value to json element

I have JSON object in process instance as variable. For example:
{
“application”: {
“some”: “some_value”
“status”: “created”
}
}
I have service task which returns status of application.
If i put into output of service task variable “application.status” it creates new varible instead of assigning into JSON object field.
How to correctly assign value from service task to JSON field application.status?