This game's modding scene deserves some attention.

This is a guide by Xgone to teach you how to extract, convert and import textures to Mario Party DS.
https://docs.google.com/document/d/1kNAaYZlhOooZ_17k7jGekTkCO4fcMukFB5wo0T4Z3p0/edit

This game's hacking scene is still very small. It doesn't have its own Discord server or forum. But for more help or information, you can join the Mario Kart DS Modding community on Discord for now. It has a text channel focused on Mario Party DS modding.
https://discordapp.com/invite/CAktUYP