how to edit initrd.img and to remake the initrd.img

bash-3.1# mkdir cpiowork
bash-3.1# cd cpiowork
bash-3.1# gzip -dc ../initrd.img | cpio -i -d -H newc --no-absolute-filenames
43980 blocks
bash-3.1# cd usr/lib/setup
bash-3.1# ls
FDhelp  INSdir      SeTfdHELP   SeTnet         migrate.sh    unmigrate.sh
INCISO  INShd       SeTfull     SeTnopart      nopartHELP
INSCD   PROMPThelp  SeTkernel   SeTpartitions  pkgtool
INSNFS  SeTDOS      SeTkeymap   SeTpasswd      removepkg
INSSMB  SeTPKG      SeTmaketag  SeTswap        setup
INSURL  SeTconfig   SeTmedia    installpkg     slackinstall

The scripts of interest here are setup and slackinstall.

After making any necessary modifications to your working copy, you need to reverse the gzip/cpio steps to rebuild initrd.img:

bash-3.1# cd ../../..
bash-3.1# find . -print | cpio -o -H newc | gzip -9 > ../initrd.img
23919 blocks