User status shift automatically?

Dear SAPIENTS,

I have created two user status:

10 NWLD lowest 10 highest 10

20 ALWD lowest 20 highest 20

Now 1st one is active i want second to be automatically active after one movement on the same screen: eg say in inspection lot screen I am attaching task list so system status getting change. Now here I want as soon as task list assigned my user status should shift auomatically to 20

Regards,

Kaushal Rai