I want to add a family house as part of a quest mod to the IC Talos district but figured the best way to do this is to take over a non-quest NPC house and mod it since I need one of the corner layouts for the extra bedrooms upstairs. I would like to know if this sort of thing is okay or not. The only thing unusual about the husband and wife living in this house is that they travel/visit others alot and (tiny spoiler:) the husband is a sleeper for the Mythic Dawn: Ulen Athram. Or would I have any alternatives if it's not okay? The home could probably be in any non-Waterfront IC district but would need to have three rooms upstairs available I can make into bedrooms.

First let me say that I like the way you blacked out the spoiler (I read it anyway).

If you are doing this mod for yourself, obviously you can do whatever you like. If, however, you are doing this for release to the community, My suggestion would be to make extra extra certain that the occupants of the house are absolutely not important in anyway what-so-ever, then after you are certain, go back and check again. Then do what you need to do to the house for your mod and in your readme file, make sure you point out who the previous occupants were, including the spoiler. Some people may enjoy hunting down "those people" and may be upset that you removed one from the game since they do not respawn like vampires.

Other than that, at the moment I can think of no reason you should not be able to jack the house. On a side note, remember that containers in npc houses respawn their contents.

Good luck with your mod.

Thanks for the feedback on this. The quest is intended for public use. If I don't see any fair arguments against this here then I'll go ahead with it. According to the uesp wiki the husband and wife are not related to any quests and offer no services. My main concern was that their being removed from the game by this mod might have any disruptive consequences, however small.

Oh and the blackout thing should be credited to the forum-makers for offering spoiler tags. I don't know if it's a new feature or not but have seen it used in the uploaded mods forum.

Ideally you should avoid changing any base game NPCs or areas if you're trying to maximize compatability with others. While merely changing the door on the exterior to link to a new interior, and disabling, or redirecting the packages on those NPCs to some standard interior, like one of the inns, has a low chance of conflicts (since you aren't editing the NPC, just changing one of their packages). It may still have minor issues with mods that involve those NPCs or that interior (since the existing interior would be unreachable.

You may however just be best off just adding a new entryway somewhere on the IC streets and ignoring how interiors would overlap if they were all in a single space (like Bethsoft did). Depending on where this new enterance is, you probably wouldn't notice it unless it was pointed out to you.

Then the question would be how important is it to most users that a new door is suddenly there and the building spaces don't match up. I like this method however since it seems like the least conflicting way to go about it. Or what about just disabling the husband and wife refs via quest script and looking for any visitor AI packages going there and removing those packages?

Suggestion:
Instead of using a house that's already part of the game (however small), there are a couple of courtyards/facades where you can just place a door to link to your cell. For example, there is a mod out there that creates a store (for exnem stuff) in the Market Plaza District where the modder put a door on an empty facade in the middle of the market plaza district ( one of the two that have 2 red Imperial City banners ) There’s another façade right across the street that you can use.