Once reviewer submits Changes Required, restrict access to make additional comments

We just tested the guest reviewers feature - which is just awesome! - and found that the reviewer went back in after hitting "Changes Required" and made additional comments. It would be great to have an option that would restrict the reviewer from being able to do so unless the document was resent to the reviewer upon his/her request for additional markup. In order to make sure our designers have captured all of the changes requested in one go, it's important that we know when to begin work on revisions based on the reviewer's one-time submission per draft. 

Please consider adding this as an option before sending to reviewers. Thank you!