For example the star coin counter, etc. Would they be found by using the No$GBA disassembler? Or a hex editor?

Also, one non-related question but since I'm here I'll ask:
What sort of complexity is required to display a text box on a level when you click A on it, saying something like "You can't enter now." It seems pretty simple compared to other stuff I can think of *cough cough yoshi* but as I've never actually done ASM before I'm not 100% sure.

Thanks.
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hey look, I did a thing

Probably with the first one
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As for the text box thing, if you found where the function for displaying text boxes is located, probably pretty easily.