The rule book states that if you build a building on the same tile as a Great Person, you put the Great Person in your "reserves" and can place that Great Person in the outskirts of any of your cities at the start of your next turn.
What if you want to remove a Great Person from one city's outskirts and place them in another city's outskirts, but you are unable/unwilling to place a new building on the Great Person's tile? Can you just pick up or reassign Great People? If so, when do you do this?
Since Trade is calculated after Start of Turn and before City Management, and since you can replace the Great Person during City Management by building a building on that tile, and can place that Great Person at the Start of Turn of the next turn, there is no loss of effectiveness by the Great Person. So I don't see any reason why you shouldn't be able to just place Great People in your reserves during the City Management phase without replacing them with buildings.
What does everybody think about this?