Does the added evidence of signature change the PDF content?

The evidence of signature, also known as stamper, seal, SVC (secure verification code) does NOT modify the content of the PDF because this is done according to the PDF signature standard

This standard determines how and where these graphic representations ( or annotations depending on the PDF data dictionary) should be used, as well as the annotations associated to an electronic signature.

In short, it does NOT modify the content. It is simply an annotation added in a layer for the data dictionary of the PDF standard