How to add and change file in bootable USB stick

"The bootable USB stick [...] is read protected"
That is nonsense. You need to be able to read the contents to boot the system. I assume that you mean "write protected".

As already written in https://answers.launchpad.net/ubuntu/+question/701214
There is a specific application named cubic that is supposed to unpack the contents of an iso installer, modify it and re-pack everything into a new iso file

Did you already have a look at it? Are there any problems when using it?

if the stick was created on a ext4, ntfs, fat32
then try this
boot into an OS that runs gparted

shrink partition one of Ubuntu stick.
add new partition, fat32, ntfs, ext4 etc..
that new partition should be r/w
I found that process is more reliable than persistance mode when creating the boot stick

Thanks Galen Thurber, that solved my question.

Hi Manfred Hampl ,
Thanks for reply
Sorry for mistakenly write read-protected.

Thanks and Regarding
        Ajay

Hi Manfred Hampl,
We are building own kernel image on the system ubuntu 20.04.4 and kernel version is 5.13.0-051300-generic and compiling kernel version is Ubuntu-5.13.0-38.43 but get below error asfollow.

CC /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/build/build-generic/tools/bpf/resolve_btfids/string.o
CC /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/build/build-generic/tools/bpf/resolve_btfids/ctype.o
CC /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/build/build-generic/tools/bpf/resolve_btfids/str_error_r.o
 LD /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/build/build-generic/tools/bpf/resolve_btfids/resolve_btfids-in.o
  LINK resolve_btfids
make[2]: Leaving directory '/home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/build/build-generic'
make[1]: Leaving directory '/home/embed/workspace/Intel_atom/kernel_5.13_v1/impish'
touch /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/stamps/stamp-prepare-tree-generic
Debug: config-prepare-check-generic
check-config: /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian/build/build-generic/.config: loading config
check-config: /home/embed/workspace/Intel_atom/kernel_5.13_v1/impish/debian.master/config/annotations loading annotations
check-config: FAIL (- != n): CONFIG_KCSAN policy<{'amd64': 'n', 'arm64': '-', 'armhf': '-', 'ppc64el': '-', 's390x': '-'}>
check-config: 11084/11085 checks passed -- exit 1
make: *** [debian/rules.d/4-checks.mk:25: config-prepare-check-generic] Error 1

Please help me.How to solve this issue.

Regarding and Thanks
          Ajay

I am sorry, I have no idea what the cause of this problem is. I have no experience with building own kernel images.

A short web search for some messages from your output indicates that KCSAN needs gcc version 11, but I assume that you have only version 9.

Hi Manfred Hampl (m-hampl)
Thanks for reply it works for me.