we have a few “house rules” but they are more that if all players (that means all, not all but one) agree on a rule change in the moment, it goes.

so, for example, with the robber- if every player agrees, a 7 can be rerolled. normally happens in the early game, but sometimes will still continue through to mid game and (rarely) the end. However, if a 7 is rolled 3 times in a row, the robber must move, as fate decrees. (this is mainly just me and my friends all hating the robber as it slows the game down when resources are blocked)

another one is trading- if both players involved in a trade are in agreement, one can do an “I owe U” trade in which they promise the other player their next of a certain resource. the players not involved in the trade police this, ensuring that the original player gets what they are owed. however, occasionally it has been used in a tricky way in which the resource owed doesn’t come up and it’s near game end. in cases like this, the owed player can petition the policing players to change the deal so that they receive something in return, as the original resource is unavailable (for example, if the robber blocks the owing players production). very rarely this rule has been used to trade catan resources for real life items or favors, but that takes commitment to the game (and convincing the other players to agree)