So I want to restrict access completely while I do some major editing on a website. In fact I just want to allow access from a single IP address. Well that can be done by editing the .htaccess file in your web-directory. If you have cpanel you can edit via the file manager. Also I found that the litespeed webserver uses an otherwise by Apache depricated way of controlling access.
# BEGIN ACCESSCONTROL
# Deny all but allow one or more ip addresses
order allow,deny
deny from all
allow from xxx.yyy.zzz.vvv
# END ACCESSCONTROLWordPress Access Control via .htaccess