@Nicholas Kosner:
I think you misunderstand the IOS used to make the wad manager function properly on the Wii
and the place where the forwarder is installed to.
The Forwarder doesn't install to a IOS slot. it doesn't replace a IOS at all.
The IOS that you select in the WAD Manager is used to gain access to the NAND (memory of the Wii) in order to install the forwarder on the Wii.
The Forwarder's data will then be installed in the "Channel place" which will appear on your Wii system menu.
When you launch the Wad Manager, select a IOS which will provide you access to the internal Wii storage.
It can be a cIOS (cIOS 249 or 236 for example), or an official IOS coupled with AHBPROT patch (IOS58 is commonly used as it's the one used by the homebrew channel, and the AHBPROT patch is provided by the homebrew channel).
What you choose depend on the homebrew you are using and its version.
Recent versions of the wad managers don't need any IOS selection anymore, they can access the Wii memory without problem.
Use a wad manager, install your WAD and see if it works.
If it doesn't work, maybe you need a specific IOS to gain access to the Wii. in that case only, you may need to reload to IOS 236 before installing the WAD file, or update your manager!