While possible to do on Tiramisu, it is highly recommended to use Aroma so you can load the themes automatically, and since SDCafiine on Tiramisu is very outdated
Using ThemeMii is NOT recommended, as it has been known to cause bricks
Loading Custom Themes
Custom themes can be loaded using SDCafiine
What you need
The latest release of SDCafiine (the Tiramisu version can be found here )
Download and extract the .zip file and drag the wiiu folder to the root of your SD
A backup of your Men.pack and Men2.pack files
You can create a backup using Theme-Manager ONLY use this to create a backup do NOT install themes with it
A PC with LunarIPS (or similar) installed
has been tested and works on Linux using WINE
The IPS file of the theme you want which can be found on this GBAtemp thread
Section I: Creating a Backup
Insert your SD card into your WiiU and boot into CFW
Launch Theme-Manager and press R to create a backup of your theme.
Exit Theme-Manager and put your SD back into your PC
Section II: Patching your theme files
Launch LunarIPS and select Apply IPS Patch
Navigate to your themes .ips files and select Men.ips as the patch file
Locate the Men.pack file in the sd:/wiiu/themes/backup folder on your SD and select it as your base file
Repeat for Men2.ips and Men2.pack
Section III: Prepping files for SDCafiine
For SDCafiine to load the files you will need create the following folders:
Create an sdcafiine folder in your wiiu folder on your SD
Inside the sdcafiine folder create a folder with your WiiU menus title ID. This will vary on your consoles region:
US: 0005001010040100
EU: 0005001010040200
JPN: 0005001010040000
Inside your title ID folder create a folder with the name of your theme
Create a content folder in your title ID folder
Create a Common folder inside your your content folder
Create a Package folder inside your Common folder
Place your modified Men.pack and Men2.pack files inside of the package folder
Your final file path should be sd:/wiiu/sdcafiine/[TITLEID]/[ThemeName]/content/Common/Package/Men.pack, Men2.pack
For SDCafiine to load the files you will need create the following folders:
Create an sdcafiine folder on the root of your SD
Inside the sdcafiine folder create a folder with your WiiU menus title ID. This will vary on your consoles region:
US: 0005001010040100
EU: 0005001010040200
JPN: 000500101004000
Inside your title ID folder create a folder with the name of your them
Create a content folder in your title ID folder
Create a Common folder inside your your content folder
Create a Package folder inside your Common folder
Place your modified Men.pack and Men2.pack files inside of the package folders
Your final file path should be sd:/sdcafiine/[TITLEID]/[ThemeName]/content/Common/Package/Men.pack, Men2.pack
Section IV: Loading the theme
Insert your SD card into your Wii U and boot into CFW
If you are on Aroma the theme should load automatically. If it does not ensure SDCafiine is toggled on in the plug-in menu.
If you are on Tiramisu load SDCafiine from the Homebrew Launcher
If done properly, you should now see your custom theme!