PDF and Digital Signature

Has anyone try to modify the tags in a PDF once the docuemnt has been signed? If so, how did you do it?

The problem I am having is that I don't seem to be able to add the Digital Signature object into the logic tree structure, even though my screen reader reads the important part of the object. This causes the Accessibility Checker to fail the document on accessibility. I am using Acrobat 9.

thx