I wanna replace Toadsworth's model by Toadette's one because for me it looks better when it's Toadette who is the owner of Toad Houses instead.

Well the only thing you can do is replacing Toadsworth's texture in "Romfile Browser > Root > Enemy > kinoji.nsmbd". I might help you out and make or rip some textures of Toadette.

Download:

Edit: idk if this fits, but I ripped it from Mario Party 8. MAKE A BACKUP OF YOUR ROM AND NSMBD file before converting it.

How to insert the new textures:
- Go to path I told you to go to before and open kinoji.nsmbd, and then click "Import this bitmap and recreate pallete ". Then click "Save All" to save your work,and you're done! Enjoy!
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I'm making a hack named Super Mario And The Mythical Realms !!
I also need help with it, so check it out and think abt it pls.

https://nsmbhd.net/thread/6093-super-mario-and-the-mythical-realms/