I would assume it wouldn't let you move or download the channel to your SD. Kind of like when you try do it to your NAND. Totally theoretical though because I've never actually tried,
What happens if you have all 20 pages filled in the sd card menu and you try adding another channel/vc/ww into it?
if there is no space for it it wont get moved it will error out .....
just get a bigger sd.....32GB is max
I know you have the HBC installed on your wii. Just use Triforce and launch all your VCC games from your hd.