You can spawn an NPC, but that could break your save later on because the game isnt over after all.So, no NPC spawning command, or set quest stage?
If so, I lost over 40h of gameplay
I guess you can check on the .XML save file the IDs of the NPCs by "ctrl+F"... Given the .XML indexing structure is the same as the base game
As far as Commands exist for quest stage IDK any.
EDIT:What I mean by breaking is you can have the NPC but storywise if are spawning because for example you killed takumi or whatever then you cant revert that. The npc will be there but story will treat it as dead I assume