/KNOPPIX/usr/sbin/rebuildfstab

Script for creating the /etc/fstab file

Every time Knoppix is booted, there is a script to create new "/etc/fstab" file with "ro" (Read only entry).

Perhaps you can modify this script in order to put "rw" on /etc/fstab, every time Knoppix rebuid fstab.

Other solution is to create 2 partition on USB, one is read only, the other is read-write.