Can I change story lines after starting one already?

So I used to play this game years ago and already have two characters that are around lvl 250.

When I first started it was a lot different in that there wasn't really a tutorial area with portals like there is now. Before it automatically just threw me in Vvardenfell because I bought the Morrowind game edition.

Now yesterday I started a new character and ran through the tutorial to refresh my knowledge and when I got to the portals I went through the Vvardenfell one.

Except today doing a couple missions I now remember this quest line and decided I wanna do one of the other 3 instead. Is there a way to go back to that portal room and go into a different one to prompt a different quest line? Or do I have to just create a new character again?

Also side question: Is there any other extra DLC I should think about getting that is worth the price? All I have is the Morrowind DLC with the Necro and Warden class DLC.

TIA