It's certainly possible but it would require a team of modders, several voice actors, and a heavy rewrite of early quests, triggers, and the accompanying scripts. Maintaining continuity would be hard, also not to mention that when they finish the new 'dynamic' start, it would be a noticeable change when the player gets forced back into the default Fallout 4 progression system. To sum it up, you can't just really keep it at the opening missions, a project like this would have to span to every quest in game just to preserve continuity and immersion, and that's just simply to much work for most modders to commit to.