Results are generated on the server when you submit your post. Previewing or refreshing does not give you a new result, the animation always ends on the saved result.
Regular members cannot replace or remove a locked roll by editing their post. Copying another roll shows a warning that it is a reused result as shown.
Every generated roll is recorded with the member, post, result and time/date. Those records remain always available to admins even if the post is later deleted. An authorised staff reroll preserves the original result, records a reason and marks the replacement as 'Staff reroll.'
However, members can add more rolls, currently up to five per post, and create new posts. Attempts to change a locked result are blocked. Deleted posts or hidden formatting can make previous results less visible to other members, although the records remain.
So admins/staff can investigate repeated rolling, but the system does not enforce 'one attempt per RP action.' at the moment.
Looking for feedback on this one as well.