Let's face it as a game master in a busy world, we don't have a lot of time to always come up with our own setting. To our rescue many times is the established setting. Sometimes even, the game has such a setting implied. Take the game I've been playing a lot of, The Savage World of Solomon Kane. The whole point of the game is to play in the setting of Solomon Kane. Of course other times, it's also the de facto standard setting for a system. In Traveller, the Imperium is such a setting. While you can play games outside that setting, all the rules and supplements are going to be based on it.
So with all the pressures of time and the wealth of information out there for established settings, why on earth would you want to even bother to tweak the setting?
First off, let's face it. If it's a good setting, then your players may have read all the material. Let me give an example. As a person who has played Traveller and run Traveller quite a bit, I have read most of the Classic Traveller material out there. Which means that if I was a player, I would likely have too much meta-game knowledge. As a good player, I would not try to have that influencing how I play my character. Still, I'm sure in small ways it might. As a GM, having a player like that could ruin what I'm trying to run. This can be especially true if the player has read things that you the GM hasn't read.
Second as GM, we do like to invent things. Which means we want to make our own mark on the world in question.
Third without knowing it, you are already tweaking an established setting. Yes that's right you are. Just by using the material, the GM and players are making their own interpretations of the material presented. Let's use a simple example, maybe the description for an NPC king says that he's sad about the death of his daughter. Now the material may give examples of how that's effected his kingdom. Still as GM, you will have to decide how that NPC may act in the front of the players if it's not already stated. All of which means your sad king may act differently than another GM's version of that same sad king. Congratulations, you have already tweaked your game and didn't know it.
So what sort of tweaks can you as the GM make easily?
• Change the Names of certain places.- Change the name of Inn or tavern or move where it is.
• Add/Change/Delete NPCs in the setting. - Maybe flesh our that sad king's adviser
• Add/Change/Delete monsters and their treasure.
• Flesh out locations
No matter what, you need to let the players know that just because they have read the material doesn't mean you haven't changed it in some way. This will prevent arguments in the future. One should always be on guard against fan boys and girls.
One word of warning. If you use an established setting, please don't expect your players to have read 60 pages of setting background. If you do, you will be disappointed. Create a one to two page summary if you can.
Just remember, it's your game and you get to do things you want to do. Using an established setting is just a jumping off point that prevents the GM from having to creating everything.
Update: I forgot to include a link back to original Blog Carnival Post. So, here it is.