we are generating a correspondence document for that we are using a Flow action. 

Flow action name will be "Create Document". But our requirement is to give bit more specific name like "Generate Person Document" "Generate Additional Document" . 

I don't wanna create separate flow action for these. So wanted to make it dynamic. 

I tried setting the value to newAssignPage.pyCurrentActionLabel in the pre processing DT of that flow action. 

But the value changes only after i refresh the page. 

If you have conditional then you can achieve it by creating control and referring it in filed value.

Syntax for referring control in field value is 

Constant text.
Hello {.Name}

Uses a property reference and either the control defined for the Name property or the Default control.
Hello {.Name MyHTMLProperty}

Uses a property reference with an explicit control.
Hello {1} and {2 MyHTMLProperty2}

Uses two parameters. The second parameter uses a control.
Hello {.Name NameHtmlProperty }, {1} and {2 htmlproperty2}

and in the control I have written the code as below

<%
  ClipboardPage pyWorkPage = tools.findPage("pyWorkPage");

  String pyLabel = tools.getStepPage().getProperty(".pyLabel").getStringValue();

  if (pyLabel == "Image 1") {
    tools.appendString("Image 1");
  }

 if (pyLabel == "Image 2") {
    tools.appendString("Image 2");
  }
%>