Manually creating a WAD file is no longer necessary with the new web-based randomizer! These instructions have been maintained here for reference, but you should use the website to generate a WAD file instead of this manual method.
These steps are specifically for a Japanese randomized ROM. This WILL NOT work with a US ROM! For a US ROM, use the other method.
For obvious reasons, we can't tell you how to get this. Suffice it to say, you need to find the WAD file for the Japanese Super Mario RPG Virtual Console release and download it.
If you don't already have it on your SD card, download the YAWMM.zip file from here: https://code.google.com/archive/p/yawmm/downloads
Unzip the file, and copy the apps folder to the root of your SD card, and merge it with the existing one. Basically you want the WADManager folder to be inside your apps folder.
Download this ZIP file: http://www.mediafire.com/file/2u2a6flult51ca1/WAD+Editing+Tools.7z
Extract the contents of the ZIP file anywhere in your computer. You should have a bunch of files and a folder called Auto Injector. This is what we will use for the Japanese ROM.
Put the randomized ROM and the Japanese VC WAD you downloaded into the Auto Injector folder.
Run the Auto Injectuwad Injector v3.exe program.
You should see the list of WADs in the current folder on the right side of the window, and the left side to select a ROM to inject should be blank. Click on the Console Mode menu and select SNES, and your ROM file should appear on the left side.
Select your ROM file on the left, and select the Japanese WAD file on the right to inject it to. In the Output.wad section, you'll see the output filename of the WAD file that will be generated.
At the bottom, you need to fill in the Custom Injected Channel Title text box with anything you like. This will be the title that appears for the channel on your Wii menu once it's installed. A good idea would be something involving the seed number to identify it, such as "SMRPGJ <seed>".
Press the Start button and a command prompt should open as it injects the ROM into the WAD and packs it.
In the root of your SD card, create a folder called wad if one doesn't already exist. This folder MUST be named "wad" exactly!
Copy the injected WAD file you generated in the previous step to this folder, and insert your SD card into your Wii.
Load up the Homebrew Channel, and open YAWMM.
Select IOS249 as your IOS, and leave "NAND Emulation Device" disabled.
Select your SD card as the location where your WADs are stored, and it should list the files in the wad folder we created earlier.
Select your injected WAD file you just copied to this folder, and select Install and it will install it.
Exit the Homebrew Channel and go back to your Wii menu, and your randomized WAD should be present in your channel list with the custom title you entered! Enjoy!
OPTIONAL: You can get a SNES to GameCube converter to play with your actual SNES controller: http://www.raphnet-tech.com/products/snes_to_wii/index.php