plural ad·den·da \-ˈden-də\ also ad·den·dums
Latin, neuter of addendus, gerundive of addere
1 : a thing added : addition
2 : a supplement to a book —often used in plural but singular in construction
If you click edit, it lets you change the entered text and puts a discrete edit footnote if you enter a reason.
If you make a second post before anyone has replied, it will add the second post to your first as an addendum, rather than creating an extra post.