Map markers for Far Harbor and Nuka World enabled from start. You will still need to travel to both locations the normal way the first time, then you can fast travel within the DLC map.
IMPORTANT QUEST NOTE
You MIGHT break some quests by directly fast traveling to a quest location vs traveling to it the way you were normally intended. If a quest doesn't trigger try walking away from the area and then returning.
If you want the vanilla only version of this mod try these mods by LBGSHI