I don't understand what you mean.
making partition on an SD card? the Wii can't see SD card partitions.
Why do you think you need different partition for each games?
cheatcode can be on SD and games on USB on the same partition, you don't need different partition for each game, nor for each cheat code.
cheat code are text files, you can have all the cheatcode for all your games in the same folder at the same time.
Are all the 3 games you mentioned some kind of modded version of the same game, and sharing the same TitleID?
If it's what I think, why would they all still use the same official game's TitleID and not have their own like "newer mario bros" ?
If they share the same TitleID, then it's problematic, and switching might be one solution.
Another solution could be different usbloadergx folders, with 3 different settings pointing to 3 different "cheat" folders.
The best solution is to only have one usbloadergx on SD card, and 3 usb partitions.
go to settings > user settings > cheat path, set the path to use based on the game you want to play.
go to settings > hdd settings > install partition, click on it to switch the USB partition to list. do not use "multi-partition" option or it'll detect the same TitleID and list only one game.
a little annoying, but it's the second safest method after "switching different SD cards".
Having 3 different USBGX on the same SD card could work and be easier, you only launch the correct one from HBC based on the game you want to play, but it can cause conflicts if you are not sure how everything works.