Right, a few hours ago I decided to try fucking around with Soku using Cheat Engine.
The giant catfish is completely unplayable. The very moment you start the match it crashes.
Same goes for the giant doll.
In arcade and story, the game can be changed to 2P mode, except when player 2 dies, there are no spellcards. The level moves on as if you've defeated the character. This works with Sanae and Cirno, but not China; it crashes when the fish is supposed to appear.
If you change the game type to practice or VS com in story or arcade, you will be controlled by the computer, with the difficulty at the same level as the opponent.
The best part is the character values. If you freeze it on the character you want, you can play through story with everyone except Utsuho and Suwako. It loads the character's SWR story, complete with the old-style dialog. You can play it right up to the end, but when Tenshi uses her spellcards where she makes large rocks appear from the ground, you cannot land on them, you just hover as if falling; if Tenshi manages to catch you in the first one, neither of you will be able to move. If you stay on the ground in the second one, Tenshi will be the only one who is frozen, and you can just hit her with long-range moves.
After defeating EX Tenshi, the game will stop responding (this is what Pasonia may have been referencing), but fortunately, you can still save replays if you die or quit, and they will be viewable by anyone.
HP cannot be hacked. Only that little red afterglow can, and you still die when the bar runs out.
Stages can probably be hacked, but I don't care so I haven't bothered. Same goes for weather.
...maybe I should write a guide for this...
Also SiN, why have you not unlocked Utsuho?