"Change nation rules" only lets you add new lower leagues to existing nations. So if you want to change anything about the top four tiers of the Swedish league, you will have to "add nation rules". Unfortunately you then also have to recreate other things like prize money, promotion/relegation etc., so you might want to consider whether it's worth it.
A way to get around it might be (and I'm not sure if this will work) to go to "Nations" -> "Sweden" -> "Nations not counting as foreign" and add literally all nations...