How are they going to do this?
Once the ballot is received and separated from the signature cards, there's no way to invalidate a particular ballot.
If they segregated the mail in vote tallies from the in person vote, one might be able to get a total of all fraudulent votes and subtract proportionately from the mail in vote tallies.
If the mail in vote was mostly fraud votes for Buydim, this could help swing the calculated "legitimate vote" back to Trump, I suppose.
Mainly I see this as a cover your ass move by Kemp to try to keep from getting unseated in his next election by pretending to do what is "fair." He sees the writing on the wall and was likely scared shitless by Sidney Powell's announcement that she was going to blow up the Georgia election mess early next week.
As the corrupt state and local officials start see the writing on the wall that, we indeed, know what they did and how they did it, expect more last minute "come to Jesus" moments where these local yokels start trying to cover their own asses and start back pedaling.