[Gen 3 save edit] Enabling RSE-FRLG trade from the start

[BloomGloom]

The purpose of this thread is to find a way to hex edit Gen 3 savegames so that there can be trade between Kanto and Hoenn without having to beat the game.
Text in red means help is required. Text in yellow is the explanation.
Help: https://bulbapedia.bulbagarden.net/wiki/Save_data_structure_in_Generation_III

Requirements
1) The National Dex must be unlocked in each version.
According to Bulbapedia, three fields must be edited: A, B and C.
Help needed: Each save seems to have those fields in different places. How can we determine where it starts beforehand, when it's all zeroes?
I opened three different NatDex unlocked Emerald saves, and searched for the first field, which should show "01 DA", meaning the NatDex is unlocked.
In the first one, 01 DA appeared at offset A019 for Game A and 17019 for Game B; in the second one, it appeared at 6019 and 13019, and in the third one it appeared at C019 and 19019. I cannot search this way with a save that doesn't have the NatDex yet, because instead of "01 DA" there is "00 00", which is everywhere.

2) In FireRed/LeafGreen, The Ruby and Sapphire Sevii Island sidequest must also be completed.
Help needed: where are the bytes that determine its completion status?

Any collaboration is appreciated in order to make the third gen games more accessible.

Edited October 21, 2019 by BloomGloom

[EvM5_]

You would have to have access to Vermillion, One Island (meaning you'd need the first pass), and most certainly you'd have to alter one/multiple event flags to get the pokemon center on one Island to work like that. 

 

Stuff this vague and obvious aren't too much of a help (and I can't help much more than this), but what I'm trying to get at is that this is very likely to really mess with how your story unfolds later on.