Import "castle_course.szs" in the "Course" folder:

romfs\Race\Course

If your using the Dolphin Emulator to play the custom track,
use the WIIScrubber.exe to load the MKWii ISO file and replace the "castle_course.szs" file
with the custom track of "castle_course.szs" in that ISO file,
then use the Wii Backup Manager to convert the edited MKWii ISO file into a WBFS file
(Add the ISO file and the transfer WBFS file).
Once that's done, launch MKWii on Dolphin Emulator and bam, it works.


Yoshi XDD