Thanks! Most of the fixes to relationships and lore would stick to the save file itself, however there are some extra fixups and things in there that only activate when the household is first played. If a player doesn't have the mod in their game when that happens then the fixup won't happen... This mostly matters for things like Growing Together milestones, Parenthood character values, and occult fixups.
I'd probably recommend linking to the PSRO and asking people to download. I've also added special traits to the base game sims as a framework for modders to potentially add more stuff in, which could be fun :D