There are two main methods of customizing the install.  One is to
rebuild the kernel with a different selection of tools compiled into
boot.  This is done mostly by editing the file root/lib/_mkpaq which
controls the tools compiled into the bootpaq.  The other method is
customizing the optional tools.tgz.  A premade script for creating it
is included at root/lib/_toolcopy and the command build tools uses
that script to control what binaries and scripts will be added to the
/bin of the tools.tgz You can customize the initial ultra-minimal
skelton fs by working within bootdir.extras/root.  Be cautious in
modifying this or the plan9rc script may fail in unexpected ways or
the early boot environment may break.

It is also beneficial if some of the ANTS software is also present in
the main hosted environments.  rerootwin and the namespace scripts,
/lib/namespace.saveterm, and hubfs hubshell hub and grio can all be
installed to the main environment without disrupting it.