So recently my ROM hack doubled in size due to some glitch involving music, so I had to put all of its assets into a new ROM. After realizing I couldn't just replace everything, I replaced the root and would later replace "overlay9_0" with my overlay changes. After I replaced the overlay, though, my game wouldn't load so I decided to just go to the Misc. Patched Thread and replace what I replaced. After finding "Always load Boss Music," I put the offset 0x1495C, like it said, but it lead me to a random number nowhere close to what I needed to change. I then tried the European offset, 0x13FB4, to no success. After wondering what happened, I looked at the original, unchanged ROM to find the same problem. But when I looked in my doubled-in-size ROM, I found that the offset did lead to the right number. I also found that this overlay was also doubled in size, and it had the offset "B15C1C" listed instead of the "B41A80" from my original ROM. What exactly is happening here?
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Check out "New-ISH" Super Mario Bros. DS HD*!!
Renewed Super Mario Bros. still exists, though.

What exactly does that mean?
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Check out "New-ISH" Super Mario Bros. DS HD*!!
Renewed Super Mario Bros. still exists, though.

I clicked "decompress overlay" many times, though it doesn't seem to decompress overlay9_0. There are some other buttons there, so must I press one of them?
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Check out "New-ISH" Super Mario Bros. DS HD*!!
Renewed Super Mario Bros. still exists, though.

1. you don't need to transfer everything to a new rom. just open it in EFE and press "save"
2. the decompress overlay button is broken in the newest versions of nsmbe. it works fine in meromero's custom build and in old versions (I think it works fine in this one https://nsmbhd.net/download/353/).
3. when transfering code hacks, you need to replace all the overlays, not just overlay 9_0. you can do that by extracting the overlay folder and replacing the overlay folder afterwards. also replace arm9.bin, arm7.bin and arm9ovt.bin.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

Okay, you're second option kind of worked. When I got the older version of NSMBe, and tried to decompress the overlay, it said it was already decompressed. I went in with the newest version and the file size was larger. IDK though, some magic may have happened.
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Check out "New-ISH" Super Mario Bros. DS HD*!!
Renewed Super Mario Bros. still exists, though.

well those weren't really options, just 3 separate observations. facts, I guess.
EDIT: honestly though, I think the easiest solution would be to open your rom with double size in every file explorer and then just press the save button and close it. it should trim the rom.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.