Does your friend or significant other have a Mac from work that is locked down so that changes can't be made? Any attempt to make a chance in System Preferences asks for the admin password, which you don't have. Maybe they are a teacher at a school with overly-zealous sysadmins? Maybe they work at an insurance company that... just kidding, no insurance company supports Macs.
Someone Who Isn't Me knows someone that has a Mac laptop and can't print to the home printers for exactly this reason. To print at home, they generate a PDF, copy the file to a USB stick, and walk it over to another computer that can print. That is ludicrous.
Now is your chance to fix this.
In macOS High Sierra, anyone can login as "root" with empty password. When asked for the admin username and password enter "root" as the user, then leave the password blank. Two this a second time and you'll unlock admin access.
Now is your chance to install that printer, change the screen saver settings, enable Time Machine, or whatever you have been wanting to do.
Apple will surely fix this soon. You probably only have hours or days to install all the printers and VPNs and other things you've been meaning to fix.
Oh, but don't break any laws or company policies. Certainly don't create an account with admin privs, or give the primary user admin privs. That is probably against policy and could lead to productivity.
More info here: https://twitter.com/lemiorhan/status/935578694541770752
Sorry... not sorry.
And the fix is already out.