Pokedex Editing (ORAS)

[LetsGoTyranitar]

Hello everyone. I've got a small question about hacking the Gen VI games, specifically ORAS. I typically use tools such as PK3DS to make small tweaks and changes for my personal enjoyment, but I've recently branched out into experimenting with slightly more complex stuff via hex editing.

Currently my goal is editing ORAS to create a regional dex for my hack, by editing the existing Hoenn dex (swapping out existing Pokemon, changing their order etc), but I can't seem to get any changes to actually appear in game. I've determined that the garc containing Pokedex data seems to be a/1/3/2 - when viewing this file in a hex editor, you can actually find the national and regional dex orders, organized by Pokemon index number. For example, here is the chunk of the file for the regional dex from Treecko to Alakazam:

FC 00 FD 00 FE 00 FF 00 00 01 01 01 02 01 03 01 04 01 05 01 06 01 07 01 08 01 09 01 0A 01 0B 01 0C 01 0D 01 0E 01 0F 01 10 01 11 01 12 01 13 01 14 01 15 01 16 01 17 01 18 01 19 01 1A 01 DB 01 1B 01 1C 01 1D 01 1E 01 1F 01 20 01 21 01 3F 00 40 00 41 00

Now, here is my problem. Let's say I wanted to replace the Water starter Mudkip with Squirtle from Gen 1. In the above code, I replace 02 01 03 01 04 01 with 07 00 08 00 09 00. In theory, this should make the Squirtle line replace the Mudkip line in the regional dex. However, this change isn't actually reflected in game. When acquiring Squirtle, he has Pokedex number ??? and doesn't appear in the regional dex, meanwhile acquiring Mudkip gives him his usual spot in the regional dex as if no changes were made.

Is there any reason why my changes aren't actually being reflected in game?