Vim, 29 bytes

3<C-x>C╔╦╗
╠╬╣
╚╩╝<Esc>h<C-v>kkx@-Pjyy@-p

Since there are control characters, here's an xxd dump:

00000000: 3318 43e2 9594 e295 a6e2 9597 0de2 95a0  3.C.............
00000010: e295 ace2 95a3 0de2 959a e295 a9e2 959d  ................
00000020: 1b68 166b 6b78 402d 506a 7979 402d 70    .h.kkx@-Pjyy@-p

Try it online! (The V interpreter on TIO seems to have issues with exotic characters, so that link uses more mundane ones.)

Explanation

3<C-x>     " Decrement the number by 3
C╔╦╗
╠╬╣
╚╩╝<Esc>   " Cut the number (goes in @- register) and enter the "template"
h<C-v>kkx  " Move to the middle column, highlight and cut it
@-P        " Paste @- copies of the cut column
jyy        " Move to the middle line and copy it
@-p        " Paste @- copies of the copied line

Vim, 29 bytes

3<C-x>C╔╦╗
╠╬╣
╚╩╝<Esc>h<C-v>kkx@-Pjyy@-p

Since there are control characters, here's an xxd dump:

00000000: 3318 43e2 9594 e295 a6e2 9597 0de2 95a0  3.C.............
00000010: e295 ace2 95a3 0de2 959a e295 a9e2 959d  ................
00000020: 1b68 166b 6b78 402d 506a 7979 402d 70    .h.kkx@-Pjyy@-p

Try it online! (The V interpreter seems to have issues with exotic characters, so that link uses more mundane ones.)

Explanation

3<C-x>     " Decrement the number by 3
C╔╦╗
╠╬╣
╚╩╝<Esc>   " Cut the number (goes in @- register) and enter the "template"
h<C-v>kkx  " Move to the middle column, highlight and cut it
@-P        " Paste @- copies of the cut column
jyy        " Move to the middle line and copy it
@-p        " Paste @- copies of the copied line

Vim, 29 bytes

3<C-x>C╔╦╗
╠╬╣
╚╩╝<Esc>h<C-v>kkx@-Pjyy@-p

Since there are control characters, here's an xxd dump:

00000000: 3318 43e2 9594 e295 a6e2 9597 0de2 95a0  3.C.............
00000010: e295 ace2 95a3 0de2 959a e295 a9e2 959d  ................
00000020: 1b68 166b 6b78 402d 506a 7979 402d 70    .h.kkx@-Pjyy@-p

Try it online! (The V interpreter on TIO seems to have issues with exotic characters, so that link uses more mundane ones.)

Vim, 29 bytes

3<C-x>C╔╦╗
╠╬╣
╚╩╝<Esc>h<C-v>kkx@-Pjyy@-p

Since there are control characters, here's an xxd dump:

00000000: 3318 43e2 9594 e295 a6e2 9597 0de2 95a0  3.C.............
00000010: e295 ace2 95a3 0de2 959a e295 a9e2 959d  ................
00000020: 1b68 166b 6b78 402d 506a 7979 402d 70    .h.kkx@-Pjyy@-p

Try it online! (The V interpreter on TIO seems to have issues with exotic characters, so that link uses more mundane ones.)

Explanation

3<C-x>     " Decrement the number by 3
C╔╦╗
╠╬╣
╚╩╝<Esc>   " Cut the number (goes in @- register) and enter the "template"
h<C-v>kkx  " Move to the middle column, highlight and cut it
@-P        " Paste @- copies of the cut column
jyy        " Move to the middle line and copy it
@-p        " Paste @- copies of the copied line