I have read and followed Is it possible to update, upgrade and install software before flashing an image?. I managed to mount the official Arch image, synchronise the database and update the preinstalled packages. Unfortunately, it was rather slow. I think it was slow because
pacman was being emulated, which seems a little excessive.
I did a little research and
man pacman lists the following option
Specify an alternative installation root (default is /). This should not be used as a way to install software into /usr/local instead of /usr. This option is used if you want to install a package on a temporary mounted partition that is "owned" by another system.
NOTE: if database path or logfile are not specified on either the command line or in pacman.conf(5), their default location will be inside this root path.
Can we use exploit this option to install packages on a mounted image?