The Lite User Manager works well and is generally safe for the LL system. The caveats are of course there to protect your Linux Lite system, and allow multiple users to have separate home directories, and while I don't recommend changing user names some LL users may find themselves wanting to. Choosing a user name at installation time can be a heady even deeply emotional thing for new users, and they may find themselves regretting their choice afterwards. The link below offers a decent explanation of the process for changing a user name in Linux.
https://linuxacademy.com/howtoguides/posts/show/topic/15014-change-a-local-account-usernameI would add to run top from the terminal for PID numbers, and to remember that the longer the system has been installed and the more applications that have been added, the more scripts there are likely to have to be edited after a user name change. Many scripts you won't find until you have a user permission problem with them. Be prepared to be annoyed if you have been using your system for some time. User name changes can be made, but because it goes deep into the core of your Linux system you will run into difficulties afterwards. Best advice: use your first name for a user name during install. You're less likely to regret it afterwards unless of course you hate yourself. In the case of a new system where perhaps you have misspelled your user name, it may be faster for you to reinstall and certainly less technical if you are unfamiliar with Linux. In LL as with all systemd systems you will need to create the temporary user to attempt the user name change.
good luck
TC
