Installing a cIOS just add a new one as IOS249.
This IOS will not be used by the Wii itself, so you don't have to worry about that file on your wii. It's an IOS with unlocked features, used by homebrew to access Wii memory, usb2.0, etc.
Select install from network to download the IOS37 from nintendo server, or put the IOS37 original wad at the root of your SD card.
IOS37 will be used as base for the IOS249.
The only problem you can have is if your wii is a LU64 or up. then you won't be able to install cIOS10, just install cIOS14 then (and you will need IOS38 as base).
LU64+ (LEF100 ? for PAL) wii are protected against installation of cIOS, until cIOS11, and never install an older IOS version over another one. only newer or you'll brick.
But with a 3.3E, you are clear (it's not a protected wii), you can install it without problem and revert back to older IOS version if needed.
Are you sure your iso is not a bad dump, or a bad rerip/modified iso ?
Release Name Harvest.Moon.Tree.Of.Tranquility.USA.Wii-FATAL
Filename fatal-hmtot
And big Kahuna is only released on USA.
Do you have a region free menuloader ? or starfall ? or patched&signing the wad before installing it ?