You already found the script in the Rom which I guessed we could find. Good to know!
This is actually how I thought we could do this practically. We just have to change some parts of the Scripts here and there...
Just for example... the Egg Event. In default it appears to be a Pichu with Surf.
If we now manage to change what the egg contains... Let's say... the Pokémon Type and Moves, we're able to recreate the Event Eggs! That's basically all we have to do.
To edit the text of the script is not necessary anyway, since you already discovered the text and were the text is there is also the script, just as you confirmed now.
All we need now is some Text for the Wonder Cards!
The Altering Cave Event has flaws, just like you said.
It's because everytime you talk to the delivery guy it changes the value to the next Pokémon and you can do this until you toss the Card. That's because when you toss it and the Wonder Card and the Script gets deleted and the flag that makes the delivery visable is turned off. Therefore you stuck with the last Pokémon that was present in the Altering Cave before you tossed the card. I think this is not a too big problem, because since the Event was never released every save file stucks with Zubats anyway. But I think you're right that it could be the reason why they didn't distributed the Event. We will never know what they really were up to with this Event.
Long time ago I found the RAM location in the Japanese Versions of FR, LG & Emerald and played a little bit with it.
The RAM address is 0x020264D4 in FireRed & LeafGreen (JP) and 0x02026ABC in Emerald (JP).
0x00 = Zubat
0x01 = Mareep
0x02 = Aipom
0x03 = Pineco
0x04 = Shuckle
0x05 = Teddiursa
0x06 = Hundour
0x07 = Stantler
0x08 = Smeargle