^ Regarding tile knowledge, create an extra temporary player and one unit, destroy all the other players, change the map, recreate the players needed in the new level, then destroy the temporary unit and player ??? Assuming that the newly re-created players would have no tile knowledge at all? On the other hand, that would lose all tech advancements, diplomatic states, "history" etc. unless those can be set via lua which is not the case at this time.
Edit: Actually it might require 2 temp players or not destroying 2 players since leaving only 1 might trigger the default conquest victory. And now that I think about it, any type of Victory would have to be avoided or the scenario would end before the next level map...