How to unpack and modify/customize the initrd (using zstd compression)

script.sh

export LANG=C

TMP=`mktemp -d` 
umask 022
mkdir -p $TMP/earlycpio
mkdir $TMP/initramfs
umask 077 

cd $TMP/earlycpio
chmod 755 $TMP/earlycpio
cat /boot/initrd-5.14.21-150400.11-default | cpio -idmv 

cd $TMP/initramfs
/usr/lib/dracut/skipcpio /boot/initrd-5.14.21-150400.11-default 2>/dev/null | unzstd -- |cpio -idvm 

To repackage initrd:
cd $TMP/earlycpio 
find . -print0| cpio -H newc --null -o > ../initrd.new 

cd $TMP/initramfs 
find . -print0| sort -z | cpio --null -H newc --quiet -o > ../initramfs.img 

cd $TMP 
cat initramfs.img |zstd >> initrd.new