Moderators, IIRC, will be able to edit the custom reasons after the changes get rolled out network wide.

One thing you may wish to do is create a meta post on this asking for input([Here is ours on Physics][1]), so that you're ready with a list of reasons when the time comes.




  [1]: https://physics.meta.stackexchange.com/questions/4398/what-will-our-list-of-close-reasons-look-like