Of course the hash posting and remembering the digits would be done by a DFS client you are using. There could also be intermediares to which you "deposit" your line-ups and they post them for you once the deadline arrives - all is needed is a line-up matching the hash, no authorization from the player required.

Editing the functionality is easy as well, you just replace the hash again. It just requires a local client to do so instead of doing it on the server directly.