You can add an extra repository to include -+mkusb dus+- (__Do USB Stuff__), which will allow you to create boot usb disks with persistence of changes in a reliable way for recent Ubuntu distros such as 16.04 LTS and newer. In such distros the default traditional methods such as USB Disk Creator or UnetBootIn no longer work in all cases as they did with earlier Ubuntu versions.
Derived from: https://help.ubuntu.com/community/mkusb
{CODE(colors="shell")}
sudo add-apt-repository ppa:mkusb/ppa # and press Enter
sudo apt-get update
sudo apt-get install mkusb mkusb-nox usb-pack-efi
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And system for a tweaked version of LXLE 16.04.2 (32 bits; 1-disk-fits-all-computers approach):
https://help.ubuntu.com/community/mkusb/persistent/LXLE
But there are many other pre-built images, such as Lubuntu 16.04 32bits and 64 bits:
https://help.ubuntu.com/community/mkusb/persistent
https://help.ubuntu.com/community/mkusb/persistent/lubuntu