I found a glitch to corrupt (first) savedata, but this probably wouldn't lead to drastic improvement. Anyway, I will write what I know for reference.
First, spellbooks can also be used as two-handed weapons. To do so, equip a spellbook as an item, encounter an enemy, and exchange your weapon for the spellbook. The effects of spellbooks vary, and some of them make the game freeze after chacacters attack with them. But spellbook of Fire is very strong (it works like Blood Sword).
And, if a character fights using a kind of spellbooks, the skill of another character (after him) is trained. So, if the 2nd-4th character does it, the memory out of range will be changed. By the way, savedata ($6300-) exists right after skill data ($6200-). So we can corrupt savedata using spellbooks.
Here is the table of spellbooks to corrupt savedata:
# Spell Skill TargetAddress
Fire magic[0] of next character $6310
Stun magic[0] of next character $6310
Minimum magic resistance of next character $6332 # freeze
Blink ? of next character $633A
Esna axe of next next character $630C,$634C
Forg spear of next next next character $6308,$6348,$6388 # freeze
Wall spear of next next next character $6308,$6348,$6388 # freeze
Clouda spear of next next next character $6308,$6348,$6388 # freeze
Toad spear of next next next character $6308,$6348,$6388 # freeze
Haste spear of next next next character $6308,$6348,$6388 # freeze
With these books above, we can modify the addresses below:
$6308 Chokobo state (1:exist, 2:riding, 3:permanent)
$6309 Chokobo x
$630C passenger ship state (2 or above:can be taken, even:route1 odd:route2)
$630D passenger ship x
$6310 player x in the overworld
$6311 player y in the overworld
$6332 chest flags
$6333 chest flags
$633A chest flags
$633B chest flags
$6348 event flags
$6349 event flags
$634C event flags
$634D event flags
$6388 keyword
$6389 keyword
But, this game checks the sum of savedata on reset. So, we need to adjust the sum, modifying multiple values. savedata is considered valid when:
* sav[0x02FE] == 0x5A (this condition is fulfilled when you do save once)
* sum(sav) == 0xFF
To adjust the sum, attack/cancel trick will be useful.
Well, we can indeed modify savedata, but the values are treated as skill levels, so the format of value is limited. For x/y in the overworld, I think we can modify only y in practice.
Permanent Chokobo may be useful, but it doesn't disable encounters.
We can use passenger ship as usual ship. To do so, modify the ship state, and simultaneously push <start> when you take the ship. This is well-known as "menu glitch".
We can modify some event flags, but I think they are not so useful.
We can get some keywords, but I think it is not so useful. By the way, if you write an item-id to keyword area and "ask" about it, it looks like the "keyword" works as "item". But in fact, the "keyword" doesn't change any event flag, so it's useless.
Overall, I think this glitch is not so useful for now. We can go to Dist by passenger ship, but it seems that we need to finish all events after all.
Here is the movie performing this glitch (modifying y in the overworld):
http://dehacked.2y.net/microstorage.php/info/1142883529/SaveGlitch.fm2
