This solution may not work for the following scenario:
1) Publish form that has <MySection><MyFormElement1 /></ MySection>
2) Create a form MyForm1.xml using the above form
3) Modify the schema to add new element to MySection i.e. <MySection><MyFormElement1 /><MyFormElement2 /></ MySection>
4) Open MyForm1.xml to fill in data for MyFormElement2 but it is not possible as the element is grayed out or disabled.
How can I enable MyFormElement2 in MyForm1.xml so that user can fill in value?