change the field type

Hi,

I have two requirements

1. I have a table in a dynamic pdf form. And in the table have put a signature field in one of the cells. My question is , can I change the field type programmatically into a text field. The requirement is, if the user does not want to do an adobe esign, there is button next to the table, and the user can click on that, and in the signature field , instead of signature , the text will display "rejected by the manager".
3. There is one more table with the same layout , but here if the user clicks on the button next to the table, I want to insert a predefined adobe signature into the signature field.

    All helps are appreciated.

Thanks