You're now able to edit your plays! It should have been in there a long time ago but it's in there now. Just go to the "Your Plays" page and then click edit on the play you want to change in the bottom section of the page.
@trentellingsen has committed to make at least 1 feature or fix update to Board Game Atlas every day of 2020 (business days). Follow along here and make sure to suggest any changes you'd like to see as well!