Signatures are final - tamper proof. Go back to the last unsigned copy.
Test Screen Name is right. Signature appearance (what you see in PDF file in the place where signature was applied) is a part of the signed content and cannot be changed after the signature is created.
As to your question "[when] you create a signature can it's certificate be revoked or undone or something?", the signature appearance is not related to the certificate that you used to create the signature. Those are two separate things. Certificate is used to create a signature. Signature appearance shows some image/info in the place where signature was applied. You can create custom signature appearance in Acrobat but you need to do that before you sign using this appearance.
Whether a certificate can be revoked, it depends on the type of the certificate. If you created a certificate yourself, so-called "self-signed" certificate, then there is no mechanism for its revocation. If you procured it from a reputable CA (Certificate Authority) then CA has a revocation mechanism. The question is why would you want to revoke your certificate? Usually you do that when someone got hold of your certificate and you do not want someone else to sign documents pretending that they are you. Certificate revocation has no relation to signature appearance.