Some GameShark codes of course
Hex Editor (I prefer Hex Editor Neo)
Now let's start:
Extract the game's save state out of it's archive, it should be st0,st1,st2 etc to somewhere on your HDD (preferably the desktop)
To use get the code you want, it should start with 80 or 81. Now when you've found what you're looking for go to your calculator and add the last six values in it. Here's an example, Mario 64 USA:
Original GameShark address: 8033B177
Now remove the 80 from the code and we have 33B177, now on your calculator select HEX and add in this address 33B177.
Next click the + (plus) symbol and put value 190 and click the = (equals) and you'll get address 33B307. Since the extracted save is 10.01 MB with every game it should work with all games. (well the ones that run anyway).
After all that just open up the hex editor and go to the address given by the calculator and patch the value(s) with what you want then save it.
After you're done just put the decompressed hacked save file back into it's st0,st1,st2, etc archive and load it in Wii64.
Also note that codes that need to be frozen (80/81) will not stay frozen as this is only you writing to the file once.
However, codes that are ROM data will stay working.