You will need a Homebrewed Wii with Nintendont installed. See here for abridged instructions. These codes were authored by Minty Meeo, and this guide is basically a dumbed-down version of the one he wrote in the original download.
The easiest way to do this is to visit the Online GCT Maker. In the "Game ID" field, enter GPVE01 for NTSC-U (US), GPVP01 for PAL, and GPVJ01 for NTSC-J (JP). In the "Code Title" field, enter Cave Set Seed.
For NTSC-U (US), paste this code in the "Paste your code here" field: C224C118 0000000D 7C0802A6 90010004 9421FFEC 90610008 9081000C 90A10010 48000009 XXXXXXXX 7C6802A6 80630000 906D8228 3C808033 60848630 7C8903A6 806D9858 3880180C 38A00000 4E800421 80610008 8081000C 80A10010 80210000 80010004 7C0803A6 3B400000 00000000
For PAL, paste this code in the "Paste your code here" field: C224C11C 0000000D 7C0802A6 90010004 9421FFEC 90610008 9081000C 90A10010 48000009 XXXXXXXX 7C6802A6 80630000 906D8220 3C808033 608487BC 7C8903A6 806D9858 3880183C 38A00000 4E800421 80610008 8081000C 80A10010 80210000 80010004 7C0803A6 3B400000 00000000
For NTSC-J (JP), paste this code into the "Paste your code here" field: C224C79C 0000000D 7C0802A6 90010004 9421FFEC 90610008 9081000C 90A10010 48000009 XXXXXXXX 7C6802A6 80630000 906D8228 3C808033 60848C48 7C8903A6 806D9858 3880183C 38A00000 4E800421 80610008 8081000C 80A10010 80210000 80010004 7C0803A6 3B400000 00000000
Before selecting "Add code", ensure that you have changed the row of Xs above to the seed you wish to use without the 0x prefix. All regional versions of the game operate off the same seeds.
Select "Add codes", then "Download GCT", and save this file to SD:/codes/GPVE01.gct for NTSC-U (US), SD:/codes/GPVP01.gct for PAL, or SD:/codes/GPVJ01.gct for NTSC-J (JP). Note that the title of the .gct file must exactly match what is shown in this pathway.
In Nintendont, select SD, open the Settings menu and enable Cheats. Return to the main menu and select Boot GC Disc in Drive.
If you use the Practice Hack, ensure that you disable Cheats before running it!
