fallout-4
I play for Institute and there is a quest "End of the Line" where the Institute wants me to kill Railroaders.
There is a video where someone avoids killing them, but there is a lot of information missing how to reproduce it, I am unable to do it:
The quest is also not well documented on Fallout wiki:
http://fallout.wikia.com/wiki/End_of_the_Line
So is it possible to avoid killing the Railroaders and what are the steps to do it?
You can max out your character with 10 in each SPECIAL trait provided every time you level up you simply choose the appropriate training to increase your stats (as opposed to choosing perks).
Remember, there's no level cap, so you can keep on levelling and start getting other perks later.
So you start off with 28, but you can easily improve all of them to 70, should you choose to only train those perks starting at Level 2.
This means 70 - 28 = 42. Meaning the earliest you could max out all your stats is getting to Level 43, while every time you level up putting points in the stat you want to increase, provided you also don't find any bobbleheads along your way.
Additionally, some perks grant permanent increases in stats at specific times of the day or at a certain HP level, so those are technically also "permanent".
The Battle of Bunker Hill is a quest that is given to you by the Institute, which is why they weren't interested in being warned - it was their mission.
The reason you're allowed to inform other sides is because you'll always get this mission regardless of faction allegiance however if you're working for the Railroad they'll want informing because the synths you've been sent to kill by the SRB are in the process of being "saved"/smuggled out of the Commonwealth by the Railroad.
If you're aligned with the Brotherhood of Steel and warn them, then they'll request that you kill the synths.
At this point in the game it is possible to still be on friendly terms with every faction, if this is the case you can turn up to this mission and walk through multiple opposing factions trying to kill each other, with all of them acknowledging you as on their side.
Best Answer
If you want to complete the Institute storyline in the unmodded version of Fallout 4, you must turn on the Railroad. Once you get End of the Line, the quest will only resolve if you take one of two actions: