If you mean stuff in containers, then there shouldn't be a problem so long as you don't delete any container that was in the previous version.
If you're talking about items the player has 'decorated' the house with, by grab-moving them onto shelves, tables etc, then I think they should be ok as well so long as you don't move the tables/shelves around.
If for any reason, you do need to delete a container, don't - just move it somewhere instead and the items will stay in it. If you absolutely have to get rid of the container, move it outside the walls, and put in a run-once script to move the items from it to some other container that is accessible in the new version.
I could of course be completely wrong. Please don't take this as certain, just a starting point for the discussion.
