The surround.vim plugin allows you to wrap text objects with various
surrounding characters (e.g. ( ), { }, " "). If you have a visual
selection on 1 2 3 4 5 and type S] you will get:
[1 2 3 4 5]
That works, but if you prefer a more readable version with some extra
breathing room, you can make the visual selection and hit S[ which will
stick a space on either end:
[ 1 2 3 4 5 ]
Now, if you already have some text wrapped in square braces, like the
first example, and you want to convert it to the more spacious second
example, you can do a change surround command followed by hitting the
open square brace twice (that is, cs[[) which will convert
[1 2 3 4 5] to [ 1 2 3 4 5 ].