regular end users wont care to understand how twt hashes are formed, they just want to use twtxt! so i guess i could work in protecting users from themselves by disallowing post edits on old posts or posts with replies, but i'm not fond of this either really. if they want to break a thread, they can just delete the post (though i've noticed yarn handling post deletes dubiously...)
on activitypub i do genuinely find myself looking through several month or even year old posts sometimes and deciding to edit/reword them a little to be slightly less confusing, this should be trivial to handle on twtxt which is an infinitely simpler specification