So, I am answering to myself. As far as I understood, ISO-9660 image creates always readonly devices, when using dd.
Rechecked: When usinn Unetbootin or BalenaEtcher, the device is FAT32 formatted, then of course, write restrictions will not work. Thus, my solutions: Either use Unetbootin or, if I want to use a presetted ISO-Image (i.e. when using YUMI) , I will have to extract the ISO, edit it to my needs and then recreate the ISO (i.e. with mkisofs). Thought, I had missed something with dd. Appearently I did not. Thanks for all your help. This little issue can safely be closed. Best regards Hans
