We're now able to modify the Club Penguin games for the Nintendo DS thanks to a tool called EPFExplorer.
EPFExplorer is a tool for the Club Penguin DS games; Elite Penguin Force and Herbert's Revenge. It was made by Olivercomet.
Current features (as of version v0.9.3):
Opening and editing ARC files (Both EPF and HR)
Opening and editing RDT files (EPF. HR is viewing/exporting only, and lacks filenames)
Opening and editing TSB/MPB files. (Both EPF and HR)
Exporting and reimporting LUA scripts. (For custom mission creation.)
Editing save files. (Both EPF and HR)
Dumping audio clips to .wav (PCM or ADPCM format wav, openable if FFMPEG is installed)
Exporting and replacing music tracks in .XM format, with all sample data
The music replacing also currently has issues with some tracks (e.g. Dojo and Gadget Room, among others)
*you'll have to extract the core files from the ROM using tinke first.
Download it right here:https://github.com/Olivercomet/EPFExplorer/releases/tag/v0.9.3
Here's the very first custom mission in EPF:https://www.youtube.com/watch?v=izkaNKG4ERc