An alternative that could use switches for is to put two blank events (set to 'below hero') in front of the door and make a new page on each event with a guard graphic that is toggled by a switch. When the hero steps on the event directly in front of the door (Touched by hero), make a 'move' command for the hero to lock facing, move down (or away from the door), and unlock facing. Then turn on the switch that toggles the guard graphics and have them speak. After that, if you want the guards to disappear until the hero approaches the door again, simply turn off the switch. This set up essentially makes it appear that two guards came through the door and pushed the hero away.
If you want to add even more effect to the scene, you could make the door disappear when the guards appear to make it look like they really did come through the door. To do this, you would need to make the door an event with a second page with no graphic toggled by the same switch. When you turn off the switch, the door will reappear.
Finally, once the hero does whatever he/she/it is supposed to do to gain entry, you can make another page on each event that is toggled by a new switch so that the guards will not appear.