Edit /etc/rc.local. For example:
# cat <<EOT >/etc/rc.local
uname -a >| /etc/issue
EOT
Example #2, I have:
#!/bin/sh
# /etc/rc.local -- rc.local for Artix Linux
#
# Enter your custom commands here.
# Clear the screen
echo -ne "\x1b[2J\x1b[0;0H" >| /etc/issue
# Output hostname in ASCII art
# http://www.figlet.org/
/usr/bin/figlet -w 120 -f /usr/share/figlet/larry3d "$(uname -n)" | \
sed -e's/\\/\\\\/g' >> /etc/issue
echo >> /etc/issue
# Add uname
uname -a >> /etc/issue
echo >> /etc/issue