Edit existing event: Terra's Flashback

I want to change some details during Terra's flashback that occurs when she faints in the Narshe's mines to better fit my hack's new story. While I managed to accomplish my main objective (Replacing Gesthal with Gogo in the speech segment) thanks to Zone Doctor, the event dump and hex editing (Changed graphical action from 2A to 19 in both CC/A518 and CC/A535), there are some NPC i want to add to the scenes, but i have some doubts how to do it due to fact this is an existing event. Here is my addictions with some screenshots taken from Zone Doctor to show the new NPC's placement:

Kefka Put Slave Crown on Terra Scene:
1) Cid will added to the scene: Placed near Terra in graphical action 04 when Kefka's dialogue pops up, it will change to graphical action 07 when Kefka starts to walk (No need to add a new dialogue)

Gestahl's Speech
1) Gestahl placed near Kefka: Unlike Kefka and CO., he won't move.
2) Cid placed near Terra: His dummied dialogue ("This is my finest work....") will be restored and played after Gestahl's first one. He won't move.
3) Sprite 32, dressed up Gau (Changed to another character in my hack) added to the scene. He won't move.