++EDITED REPLY -- forgot to add script and slides
If it was up to me I would employ Adobe Sign in this workflow.
But yes, it is possible to use a script with the getField() method and hide or unhide it based on the signing action.
I would use an image field object or a text field with the word approved in a different color, bigger font size and font type. I would also make the field properties to readonly and hidden. This will allow that when the user signs the signature field, the hidden "APPROVED" field becomes visible, and when the digital signature is cleared it hides again.
Here's an example:

In the Digital Signature Properties of the signature field, I went to the "Signed" tab and ticked the radio button "This script executes when signature field is signed:" and used the line of code shown below and in the next slide:
this.getField("Text13").display = display.visible;
See slide:

"Text13" in this example is the hidden text field with the "APPROVED" word in it.
- NOTE: I also added a small custom calulation script in the "Text13" hidden field referenced below to hide the field when the signature field signature is cleared:
if (this.getField("Approver").value =="") event.target.display = display.hidden;
- "Approver" is the name I assigned to my signature field in this example to represent the signature field reserved for your last signer/reviewer of this document.
Last, if I understood correctly, you also want to hardcode the email address in your script for the last approver and all other signatories?
Can you share what code are you using to send the email to all of this recipeints?
Maybe I can help with that too.
Here's one interesting solution to handle the email portion in a dynamic fashion, from ACP Thom Parker: