I personally haven't played the game, but I've been reading about it lately - supposedly it has a rank system built into it, that makes the game harder the more advantages you give yourself, and the only way to drop it again is to die (and the less lives you have left when you die, the greater the drop). Why this is important is because the highest rank is supposed to be nigh impossible to survive on, so learning to manage your rank is part of the game. You can read all about it, and in particular the mechanics of the rank system in post 5, here: http://shmups.system11.org/viewtopic.php?t=351
What I want to suggest is that this would make a great TASing opportunity - playing around with bullet spreads that are supposed to be impossible. The goal would be one of two things: 'uses dirty RAM to play on max rank' (1) or 'achieves max rank as fast as possible on v.hard difficulty'.
(1) Note that the game also slightly boosts the initial rank with each successive game, lowering it only towards its base value with every uninterrupted cycle of attract screens - so it's possible without cheating to play starting at the max rank, but recording the whole process of starting games and suiciding would be boring.
Here's how the game looks on the max rank: http://www.youtube.com/results?search_query=battle+garegga+max+rank&aq=f
I'm not sure if it's the max rank of the v.hard difficulty or of a lower difficulty, though.
EDIT: Apparently, in addition to setting difficulty to v.hard and somehow achieving the max rank, you should also activate the 'harder' mode by pressing B, Start on the title screen. I'm not sure what this changes specifically.