I think you need to use another JoltTransformJson processor and keep your desired order of fields in this processor.
in the above example i have jolt spec with key values specified which order i need to get them in the resultant flow, same way you can keep your desired order in the second JoltTransformJSON processor.
You can also try using JoltTranfromRecord processor starting from NiFi-1.8 where we can specify Record Reader/Writer controller services as we can have desired order of fields.
In case if you are adding only one key/Value to your json message then consider UpdateRecord processor and keep your default values for Flag field and specify RecordReader/Writer controller services in this case you can add the field and arrange your fields in the desired order using only one processor.
Refer to this link for more details regards to UpdateRecord processor usage.