The perceus initramfs.img is a standard initrd. To modify an existing one use these steps:

1. Make a backup copy

[root@perceus tftp]# cp initramfs.img initramfs.img.backup

2. Create a directory to hold the working initramfs contents and unpack the initramfs into it

[root@perceus tftp]# mkdir myinitramfsdir
[root@perceus tftp]# cd myinitramfsdir/
[root@perceus myinitramfsdir]# zcat ../initramfs.img | cpio -idmv
dev
dev/pts
dev/pts/0
dev/pts/1

3. Modify whatever you wish to modify.

4. Repackage the directory into an initramfs image

Perceus gets developed on Red Hat Enterprise Linux (via rebuild projects) and Caos Linux. Other distributions are supported via community testing and patches that are sent in.

This is documented in the Perceus 1.x book.