More specifically, how to edit it, so that when loading in to it or seeing its name in the main map (M) it shows as a proper clean name, ex "The Lost Islands" instead of "The_Lost_Islands_01" ?

Create any entry into the Translated String Key. I usually have a separate one for level names.

Give an entry the name of your exact level name, must be The_Lost_Islands_01 exactly.

Then on the 2nd column you can name it whatever.

Thanks Sniper, you're a champ! Will try it.