Huh? If you have any stack exchange points you can just edit the answer and move on. If you have like 500 points or so on one site you automatically get privileges on all the others.
As some higher-up comments have stated, since the answer is Closed as duplicate, it is more limited to interaction than a regular open answer.
Also editing an answer to something completely different is definitely not in the right way to "solve" bad answers, I think. My guess is the edits would be revoked, in any case.
