How do I make a cheat-code permanent on Knoppix 8.6.1?!

Summary:

How do I make the following cheat-code permanent on knoppix 8.6.1 on usb stick,
because filesystem type is iso9660 (read-only) and won't let me edit
/mnt-system/boot/isolinux/isolinux.cfg.

Cheat code entered at boot prompt: knoppix xmodule=vesa

Full Details:

I've just put knoppix 8.6.1 on a usb stick (persistence was there by default).
But X Window won't display unless I enter the cheat-code "knoppix xmodule=vesa"
at the initial boot prompt.

Incidentally, when using Knoppix 7.7.1 on a usb stick, on the EXACT SAME laptop
(Acer Aspire 5755G), I don't need the cheat-code.

I'd like to not have to type the cheat-code in every time I boot the 8.6.1, and
believe that I can achieve that by adding "xmodule=vesa" as a kernel parameter
on an "APPEND" line in /boot/isolinux/isolinux.cfg.

I can get to that file using the path
/mnt-system/boot/isolinux/isolinux.cfg.

But it won't let me write to that file because /mnt-system is mounted read
only. When I try to remount /mnt-system as read-write, it says "write-protected."

/UNIONFS is mounted as read-write, but the path /UNIONFS/boot/isolinux/ does not
exist.

I understand that because partition 1 (the main Knoppix system) is filesystem
type iso9660*, that it is by definition read-only. (*On which I believe
/boot/isolinux/isolinux.cfg sits).

Main Question: ufabetxxx

So could you tell me please, what method I need to use to make my cheat-code
permanent?

Reason for Using 8.6.1:

I'm trying out 8.6.1 because it has a newer kernel than 7.7.1, and I've read
that a newer kernel might fix my problem of downloads halting when the lid is
closed. I've already tried many lid disabling methods, but none of them prevent
the downloading from halting.