I finally made it! I tricked engine to think I am ragnarok, so I can walk on everything I want (sea, mountains). I've been hunting this for days!
Here, in FF8_EN.EXE (Steam) ASM opcode:
FF8_EN.exe+13E370 - mov ebx,[FF8_EN.exe+1C409E0] (0x0053E370)
Halfer, your memory theory is correct. Game just can't keep up so much memory (because the variables are static) and overwrites some core data that is in fact pointer and orders engine to read memory at ~0x7... (but it's unallocated, so it's null, and access violation exception is fired)
Also this:
0x020409E0 in memory tracks your current vehicle status. Here's the list:
#HEX!
00 - Squall on feet
20 - invisible low fuel car
30 - Balamb Garden
31 - *Crash*
32 - Ragnarok
Some variables makes Squall go maximally undermap, that's because vehicle doesn't exist on worldmap. For example if you rent a car, then some variable instead of digging you up to the ground just warps you to this car. Unfortunately, I lost "Blue sky car" from Balamb variable. Also warping should work on whole map (Vehicle is warping to your location). You can place Balamb next to ragnarok in seconds.