How do I modify Mule payload variables?

Question

Using Mule 3.3, I\'ve got a Payload (which starts out as a JSON and I\'m converting it to an Object using java.util.HashMap). I can access the variables just fine from a JD

Answer 1

What with:

<expression-transformer
            expression="#[message.payload.AddJob.variable2='hello';message.payload]" />

?