I don't think when mario lands on that particulat tile, the credits are triggered, instead, I think it it the level boundary which triggers the credits.
This was taken from a level editor that I have been using to look fro routes.
Although it doesn't look like it, those three rooms which look like garbage are actually the three rooms in which you battle Wario. If you were to change the block palette, it would look like an ordinary room. If you look at the balcony that Mario jumps off, the only blocks underneath are regular walls. which don't do anything. I beleive it is the level boundary which triggers the credits because that's the only other thing which Mario comes into contact with.
Anyway the save file corruption doesn't work. This is because a completed level is signified by the most significant bit of a byte (80) in memory if it is completed, and 00 if that level isn't completed. For every 00 in memory, which shows up as a breakable block, destroying it will make the value for that byte 60 which shows up as nothing. but because 60 is 01100000 in binary, thew most significant bit is unaffected, meaning that the level will still show as uncompleted.
I came up with a method which would allow me to get to the SRAM using the bat and bubble glitch, by breaking some blocks in the AE00-AFFF range. Unfortunately, this part of memory is concerned with sprites on screen, so performing the bat glitch, which basically fills the entire of the sprite memory plus more, would overwrite these blocks, and I'd be back where I started.
