Love Audiosurf? I do. Bored with the game? Yes pretty much to me as I've been a fan for almost 2 years now. But I've discovered custom game modes that keep the game still interesting & mind blowing to me. I love puzzle modes but I'm a ninja mode player for most of the time, as it is absolutely chilling & fun to me.
Here's a list of all the available keywords for you to experiment with however you want. For the ones with an X, such as [as-monoptX] put a number there, like 3 or 127. You can use many at a time, but only one from each group can be used. Note that these keywords are removed before Audiosurf sends the song's title to last.fm.
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[as-4lane] Play with 4 lanes
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[as-monoonly] Mono characters required
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[as-everybodymono] All characters have only 2 block colors
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[as-lessgrey] Mono characters have less grey blocks
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[as-allgrey] Mono all greys. Scores start at 1000 and go down with each hit.
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[as-nogrey] Mono characters have no grey blocks
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[as-monoptX] Base points for Mono characters (default 3)
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[as-nostlth] Remove Stealth and cumulative hit bonuses
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[as-swind] Sidewinder camera mode
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[as-bankcam] Banking camera mode
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[as-first] First-person camera mode
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[as-caterp] Big strings of blocks instead of only solo blocks
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[as-mszX] Minimimum match size (number for X)
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[as-wbX] Percentage of white/black blocks
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[as-mtX] Match collection ticks (default 10-25)
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[as-prowsX] Puzzle row count (0-8)
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[as-hidepuz] Play with an invisible puzzle grid
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[as-steep] For slow songs, dramatically increase slope and speed of the track (added in the 2/09 International Update)
To edit your song's tags, you could use this nice free program
Mp3tag. You could get more infos on the original page
here.