I need some clarifications...

I just started FFVI hacking two days ago and I need some clarifications about sprite change. I'm doing everything through hex editing. I want to change the sprites of the first two narshe guards that terra encounter at the beginning. These two are NPCs $10 and $11 respectively on map $13. If I look at the offset x0422D6 or x0422DF the NPC data goes like this:

B3 5E 04 00 C0 34 00 ?? ??

Logically I should change sixth byte byte from $34 to $1C (draco for instance). When I did that, the two guards still had the sprite 52 ($34).

My question is: can I change the default sprite of a character(NPC) on a map even if that character(NPC) is created after the party step on a event tile???

I could potentially use the command 37 after the offset CC/9B77 and CC/9B79 which change a character graphic set (in this particular case the command would be 37 10 1C and 37 11 1C I think...)The problem with that is that I don't have space after the two NPCs are created in the script. I can change their position or where they move but it's because there is already a command in the script for that. One solution would be to delete character(NPC) $11 and I would have enough space to change the sprite of character $10.

Am I right?

Oh yeah, my first language is frech so don't worry about the spelling/sentence structure mistakes...