Edit Narshe Esper battle

That's done via event code. Outside of using FF6Tools and/or Zone Doctor to handle events, you'd need to become familiar with the 'Event Dump', which is hosted on the wiki here: https://www.ff6hacking.com/wiki/doku.php...s:doc:game
The other event documents there are helpful as well such as the Event Command List.

Basically you'd just need to locate the event code in question and use a hex editor to locate to that code in the ROM, and edit it.
In order to find the code in the event dump, you can do a search within the dump for some dialog that is associated with the event within the closest vicinity which would lead you close to the code you'd like to edit. You'll see in the event dump all the commands commented and what not in order to go about altering them.

For the soldiers snow battle movement stuff though, that's handled by the 'entrance event' code, which you can find out easily where that is in the event dump by using a level editor and going to the map in question (016 Narshe, Ouside, Battlefield WOB) and in the event tab you'd see the 'entrance event' offset there. In this case, it shows 2CBFB, which translates to CC/CBFB. So go there in the event dump and you'll see the soldiers movement there, which you can then edit. The soldiers don't respawn btw, there's just a max amount of NPCs/objects used for that event. You can also look at the event triggers to find offsets as well, if the searching for associated dialog method fails.

So yeah the event dump along with the level editor to tell you entrance event offsets and NPC #, and of course a hex editor, is the manual way to go about doing this. I am not familiar with using the aforementioned utilities to chime in there, but I'd imagine that'd be much more user friendly than doing it this manual way, but it's all I've ever known!