I don't know if you are asking for:

1. persistence where you are doing a live uninstalled session that allows your settings to be saved.
2. install Lubuntu to an external SSD/HDD that can be booted from any computer it is attached to
3. modifying the installation iso so that you can install the same Lubuntu configuration on multiple machines.

If you are looking for persistence, then this or this article will get you going in the right direction. Many of the installers offer adding persistence to the USB live session if you do not want to do it manually. I haven't used any of them in some time so I don't know which ones offer the feature but you can look at Balina Etcher, Unebootin, Pendrive Linux's Yumi tool, or Rufus.

If you are looking for modifying the installation ISO, my understanding is something like Juju or Ansible are your solution, though I've never used any open source configuration software myself and cannot say for certain if these options are a solution.

If you are looking to use the same storage drive bootable to many computers your only real limiting factor is having to configure those machine's bios/efi/uefi for booting into Linux from external storage.