Hello, I would like to customize the Raspberry Pi Ubuntu image before I flash it to multiple SD cards. I tried to use Cubic: I downloaded the official image which is an img.xz file. I extracted it, and converted the img to iso since Cubic only accepts iso files. However, when I try to add this source iso in Cubic, it complains about having a wrong file format. Can you suggest a better way to try and customize it? I just need to uninstall some software that are there by default, and install others that are not there, nothing crazy really.