Ok so if understand correctly you have DNS pointing all URL’s from the old site to the new site so the URL’s would be this: new-site.org/?p=164
. If that is the case then the code I posted above should work in the new site’s root htaccess file, but there could be a problem with WordPress internal rewriting of p= URL’s (posts and pages).
If not and the old site URL’s are this: old-site.com/?p=164
then the only way to redirect the old site URL’s to the new site URL’s would be to recreate the old site folder and put a new htaccess file in it with the code I posted above to redirect the old site URL’s that go to the old site and not the new site. The logic is this: the old site URL’s send someone to the old site that existed before and do not send someone to the new site so adding htaccess redirect code on the new site would not do anything since the URL’s do not go/point to this new site.