divers distributions offer a way to build the system completely fresh from sources in a CLI monitor of that or from an other distro!
I did do it recently: after 48 h (the PC did not work all the time as I did start the step nights and I can not see how long it did work!) I did have a fully operable new distro entirely build out the sources. The probably most known way is to build Debian with «debootstrap» and rebuild it after that completely using apt-build (separate extension from apt-get! You have to install it over apt-get!). Divers other distro offers such experimental solutions.
Is that possible with SliTaz, not step by step one package after the next (there are about 43 packages in the Slitaz base, corresponding to «rootfs4.gz»), but with a script perhaps running by night as you are sleeping ;-) ?