Create webscenario.

Add some steps (3 steps on example)

In the 2-nd step use some POST parameters (tested only on 2-nd step).

Write some "Required string" and confirm all - Update x 2.

Then edit this scenario, go to step 2, rewrite "Required string" to some other text. Update all (x2).

Then edit this scenario, go to step 2, all POST fields will be destroyed.