Sorry the double post, but after MANY tries, I have finally found a way to get it working. I put my solution here, for if somebody had the same doubt:

Code:
script

declare_counter player
set_counter player 1
declare_counter scroll
set_counter scroll 0

monitor_event FactionTurnStart FactionIsLocal
   set_counter player 1
end_monitor
monitor_event FactionTurnEnd FactionIsLocal
   set_counter player 0
end_monitor

monitor_event ScrollOpened ScrollOpened loot_settlement_scroll
   set_counter scroll 1
end_monitor

monitor_conditions I_CompareCounter player = 1
   if I_CompareCounter scroll = 1
      set_counter scroll 0
      select_ui_element loot_settlement_occupy_button
      simulate_mouse_click lclick_down
      simulate_mouse_click lclick_up
   end_if
end_monitor

while TrueCondition
end_while

end_script
NOTE: I also did many tries before I write this topic, and I believed that I would not be able to solve it without help