You need to use a java step if you want to create dynamic properties at runtime. Following is an example code.

Suppose the property name parameter is Param.PropName = "PropertyName".

/* get the step page - if the step page is blank, this will be the primary page */
ClipboardPage stepPage = tools.getStepPage();
/* get the param value from the clipboard */
String propName = tools.getParamValue("PropName");
/* add property into the page */
if(!propName .equals("")){
  stepPage.putString(propName,propValue);
}

Note: You need to have a logic to get the propValue from somewhere.

Hope this helps.

Regards,

Yasantha