The editor won't load properly if you're using adblock or any kind of scriptblocking like ghosting. Try disabling privacy plugins on your browser or whitelisting the site (not so that we track you, but because script blockers usually don't understand when something harmless is necessary for a page to function)
I too would really like a way to edit the source code directly. On the current page I'm trying to add missing data to, as best as I can tell there is literally no way to exactly reproduce the same formatting as the rest of the page due to the "smart" editor.
Can you move the "Divine Child of Rejuvenation", "The Owl" and "Isshin Ashina" to Sekiro Major Characters and NPCs on this page https://sekiroshadowsdietwice.wiki.fextralife.com/NPCs+and+Characters ? I tried but I can't make it look good with the available tools.