Automatic box expander
Vim, 7 bytes
♥GYPjYp
where ♥ is Control-V.
The cursor starts on the first non-whitespace character of the first line.
♥G Enter visual block mode and go to bottom of document.
YP Duplicate this column.
j Move down to the second line of the file.
Yp Duplicate this line.
JavaScript (ES6), 57 53 52 bytes
s=>s.replace(/^.(.)/gm,s="$&$1").replace(/(\n.*)/,s)
Explanation: The first regexp duplicates the second column and the second regexp duplicates the second row, thus enlarging the box as desired. Edit: Saved 4 bytes thanks to MartinEnder♦.
Python, 49 42 bytes
Anonymous lambda:
-7 from xnor
lambda s:[t[:2]+t[1:]for t in s[:2]+s[1:]]
Previous version:
D=lambda s:s[:2]+s[1:]
lambda s:D(list(map(D,s)))
D is a function that duplicates the second item of a sequence.