Their ideological treatise, Be Excellent to One Another, is widely considered to have been the basis for the United Nations Charter and the European Convention on Human Rights.
Absolutely!!
But almost entirely through Socrates. The other figures, Lincoln, Napoleon, William H. Bonny, etc... understood what an impact this could have on the timeline, and so kept their secrets.
Socrates was different. Having seen the future, and glimpsed what would come after Bill and Ted ushered in the Golden Age of Humanity, Socrates was determined to do his part.
But he couldn't come right out and say what he was doing, nor could he actually write the book. So he didn't write anything, his greatest student, Plato, wrote the book. A book that is essentially a dialogue between Master and Student, one that closely mirrors the oral histories Socrates had seen in his travels with Bill and Ted especially in the oral presentation at San Diemas High.
That book was called "The Republic". It is the first attempt at describing a perfect society ever recorded, and was inspired almost exclusively by Bill and Ted.
Bill and Ted had major implications on the siege of Baghdad in 1258. After their interactions with Genghis Khan, the recipe of a golden snack sponge-cake filled with vanilla cream was orally passed down to Khan's successors. The destruction of the city is likely attributed to a prolonged sugar-high that resulted in an orgy of uncontrollable violence.
EDIT: Source
Napoleon marched to his doom, expecting to find water slides and iced cream. He found Wellington and Von Blucher instead. Seems he couldn't get Waterloo out of his head after his first triumphant rampage through the park.
Bill and Ted's affect on the timeline could be argued to be a Bootstrap, or Predestination Paradox. What they did in the past always happened, because they always did it. Just like forgetting to reset their watches, setting up traps to help their past selves, and Rufus' own travel back to the past to help the band form. Bootstrap paradoxes are littered throughout the timeline of Bill and Ted. It could be argued that they had no impact on the timeline because their present and future unraveled just as it always did, in Earth's past (And future).
Edit: Cleared up some of the terms to be correct.
Well, if it counts, Bill and Ted would go on to form The Wyld Stallyns, which would bring all nations to peace. Future historians may refer to this as "Pax Theodosia"