Decompress overlays 9_0 and 9_9 using some old revision of NSMBe (as the newest one at the time of the posting can't do that).
Open the rom in a hex editor
Use the search function to find the values on the left. Replace them with the values on the right.

Disable other main menu buttons (this means you can only get into the File Select screen by pressing A)

5C009F150010D015011081120010C015 -> 5C009F150010D015011081120000A0E3
040093E5520AFEEB -> 040093E50000A0E1

Disable titlescreen cutscene (timer is at x21C7AFC, x200A4DC is where the jump to "Check if B pressed" is done)

2183E00BB220D2E1 -> 2183E00B0000A0E1

This is for the US rom.

EDIT: Updated the titlescreen cutscene skip, because the old one broke the opening scene.
This makes the game think you're constantly pressing B on the titlescreen.

Cool!

Maybe you'd want to take a look at NSMBe ASM patch compiler/injector: tutorial How ASM hacks are setup. It makes writing hooks that modify game's functions or add your own code really easy.

Also the address 0x021C7AFC is in the heap, it won't be constant. (Heap starts at 0x021901E0 in US rom)

Indeed. It's a timer that increases by 1 each frame and is checked by the game each frame on the titlescreen. If it's big enough, the cutscene starts.
I just made it increase by 0.

I mean that the address won't always be constant. It's probably a field in the titlescreen actor class (or another one), which is dynamically allocated. It can get allocated in another place in the heap depending on the order of stuff.

Anyway if you've modified the code that modifies it, it should be good

You may also want to check out the IDA Pro DB in the uploader, it has many stuff already documented.

Oh, I see. That's indeed possible.

How can I insert this into the ROM?
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Thanks
~~~Stunt_LP~~~
ASM Hack we're making in the moment:
- Info Block from SMW
It will be shared with the community

First decompress all the overlays within the rom, open it in a hex editor like Hex Workshop, press Ctrl+F, paste the code from the left, press find. It should find one instance of it in the rom, change it to what's on the right and save.

I decompressed it but it says that it can't find the code.
_________________________
Thanks
~~~Stunt_LP~~~
ASM Hack we're making in the moment:
- Info Block from SMW
It will be shared with the community

I should perhaps mention that the latest NSMBe cannot decompress overlays.

See a lots of creative DS Hacking here
If you want to support me, you might check out my Patreon Page : )

The button to do it one overlay at a time is there, but it just doesn't do anything.

If I decompress it in a older version it writes "Unable to decompress. Maybe that file is already in it's decompressed form." But it still doesn't work.
_________________________
Thanks
~~~Stunt_LP~~~
ASM Hack we're making in the moment:
- Info Block from SMW
It will be shared with the community

See a lots of creative DS Hacking here
If you want to support me, you might check out my Patreon Page : )

Button stuff should be at x141A5C0 and x141A504
TS CS stuff should be at xBE60

If they're not there then either the overlays aren't decompressed or the ROM is somehow different

See a lots of creative DS Hacking here
If you want to support me, you might check out my Patreon Page : )

Honestly, not sure.

As long as your hack doesn't modify this precise bit of code (which is very very unlikely) you should still see this hex string and be able to replace it.

You have to decompress ALL overlays though. The ASM patcher only decompresses the overlays it needs to patch your code.

The codes skawo said are probably in Overlay 9 (Titlescreen overlay) so maybe decompressing that one will be enough to find the stuff

Anyway if you're combining this with other ASM patches I suggest you convert this to .s patches and apply them with the rest of the patch. Otherwise you're going to have trouble, because the editor restores unmodified copies of the overlays and binaries when applying your hack again, so it doesn't apply the hack over itself (would break things) so it's maybe reverting your changes :|

See a lots of creative DS Hacking here
If you want to support me, you might check out my Patreon Page : )

I can't find anything that I want to find in overlay9_0 after searching multiple times. Though this may be a stupid question, would it be okay if someone uploaded an overlay9 with the titlescreen change in place?

It wouldn't be overlay9_0, it'd probably be overlay9_9.

EDIT: In fact, I just looked, and indeed it is there.