I'm looking to correct a choice I made almost a hundred saved game files ago for Xoti where I selected the dark choice instead of the light. Is there any way to edit a saved file/questline progress where I can fix? I delete my save files so reloading isn't an option.

It's not a problem if you selected the dark path option once (or twice). 

For every option during your quest dialogue there will be +1 point to either the light or the dark side. 

Once the quest comes to an end the game will look whether you chose light or dark options only - then the outcome will be clear. But if you took some light and some dark options you can influence the outcome during this last stage of the quest. Only if you took dark options exclusively until this point you will be locked into the dark side. 

For more details read here:

https://pillarsofeternity.fandom.com/wiki/The_Lantern_of_Gaun

You have to pay close attention to the explanation at the end: it's a bit counterintuitive to get the outcome you want. However, I think that's a much easier solution than trying to alter the savegame. 

Run these two console commands (skip iRoll20s if you've already enabled cheats)

iRoll20s
SetGlobalValue n_xoti_light_or_dark_alignment 1