No. If foo@1.2.3 is already published, you can not overwrite foo@1.2.3 - you'd publish foo@any.other.version (typically something at least ^1.2.4) and mark foo@

No. If foo@1.2.3 is already published, you can not overwrite foo@1.2.3 - you'd publish foo@any.other.version (typically something at least ^1.2.4) and mark foo@1.2.3 as deprecated (which won't actually make it unavailable like an unpublish would).