I would like to report that I conducted the final exam for my course using Tim Hunt's deferred feedback with explanation question behaviour plugin (get your copy from: https://moodle.org/mod/forum/discuss.php?d=273004#p1179166).
It worked like a charm.
I know I have expressed my appreciation when he wrote the plugin but this needs to be reiterated - it worked beautifully in practice.
Thank you, Tim!
PS: If you could just give the instructor the right to edit the standard text before that text box, it would be greatly appreciated. "Explain your reasons" works well but there could be usecases where we wish to inform the students differently. I wanted it to read "Enter justifications below if you want partial credit in numerical problems by showing your steps, ignore otherwise.".
I did it verbally with the students, and also in the instructions to the exam, but some still forgot, and either failed to use it entirely, or got conned into adding explanations for even true false questions. Given how little listening some students do, I can't say I was surprised
But this is just a minor issue and not something you should worry about unless it is super easy to do. You have already done the Moodle community a huge favour.