so AFAIK the only thing that would be possible in the current protocol would be to have the originating server you posted it on stop adding new replies to the post's metadata and reject the AP messages when they come in
... which due to the mentions mechanism, would create an ironic result: everyone sees "locked replies" *except* you (and the originating server for the replies)
But perhaps in conjunction with a mute, that would be a sufficiently effective deterrent in your opinion?