How to get a new image with extra stuff installed

I needed to have a new craff file after I installed gmake and gcc onto the simulated disk.
The easiest way to install these files into a RW disk.
To do that, you need to boot your virtual machine using something like the following:

# set up 1 processor with 256MB, unless other given by
# user setup variables
@boards = { 0 : [[0, 1, 256]]}

# do auto-login per default
@if not "do_login" in dir():
do_login = 1

# tell sarek-common that we are using the disk we just
# installed solaris 10 onto ourselves.
@sarek_disk_size = 8589934592L
# IMPORTANT This is the line that makes your disk a RW disk.
@sarek_files = [["sarek-solaris10.craff", "rw", 0, 8589934592L]]
#@sarek_disk_size = 4256972800L
#@sarek_files = [["sarek-solaris9.craff", "ro", 0, 4256972800L]]

# the rest is common for all sarek machines
run-command-file "sarek-common.simics"

save the above into something like gold-1p-sol10.simics
and boot your virtual machine using that.
Then install stuff in that session and after you quit, all the changes you made will be persisted into the RW disc, which is named as sarek-solaris10.craff here.

One thing bear in mind is that the checkpoints made with the sarek-solaris10.craff before WILL NO LONGER work. All checkpoints must be retaken.