Event Hacking - What am I doing wrong?

Program: Zone Doctor CE 2.2
Rom: Final Fantasy 3 US 1.0 Headered
Checksum: 0x81E7 (Fail)
Gamecode: F6


I've started into event editing for my hack using Zone Doctor CE. Most of the events that are edited are very simple; I just need to point the lines and actions of one actor to a different actor. No additional bytes; good to go.

The problem comes when I try to edit scenes where I have add or take away characters or actions. For example, in the banquet with Gesthal, I have Banon replace the generic soldier that seats you, then take the middle seat at the table, with the party characters sitting on either side of him. On the other side of the table are Gestahl, Cid, Celes, and 2 elite guards. Just by changing where Cid sits, I was able to remove exactly 32 bytes of "turn left, now turn right" character actions. The event plays out exactly how I want it to without error. The problem comes when I need to load the next event (make a toast). Even though I re-pointed those specific code branches, and Zone Doctor CE repointed all of the branches from those events, each of the 3 options crashes the game in a different way. Locke (party character 2) goes into spasms, and then the game crashes.

I've tried this for a few other scenes too (naming Leo as character $0D in the Military Base Camp, adding Banon to your party after the Banquet), and it almost always has the same effect. Zone Doctor CE seems to be auto-adjusting all pointers, but the rest of the game gets thrown off. NPCs don't say their correct lines, and the wrong events get triggered, and exits do not load new maps, often leading to the game locking.

I will be the first to admit I'm new to this, so what am I doing wrong? Do I need to edit these scenes so that I have the exact number of bytes as I started with in each one? In all, I will need to re-do around 15 events spread out over the entire game. If I have to manually re-point every NPC and exit tile in the entire game, I'm going to lose my bloody mind.