You can change any of the signers on the Audit page for your Sign Request which will reassign any of the fields assigned to them. Just open the Sign Request document and click on Manage and Audit in the upper right or add “/audit” to the end of the URL and use the Signer Actions menu next to the signer you want to change and choose Reassign Email Address. The article below explains more:
How do I send my PDF as a Sign Request?
As for editing a document after it’s sent as a Sign Request, you’d need to make a copy on the same audit page using the Document Actions menu, or edit the original (if it’s a Template) and resend it after making the change to the content. Or, if you just need to make additions to it, there is an option to add annotations after sending a Sign Request but only if you enable the option for Can Annotate in the window before sending it. You’ll see a switch next to each signer to enable the ability to annotate the document.